A brain like a BB in a boxcar.
A couple of bricks short of a hod.
A couple of knights short of a Crusade.
A couple of togas short of an orgy.
A couple of volts below threshold.
A couplet short of a sonnet.
A day late and a dollar short.
A few beers short of a six-pack.
A few birds shy of a flock.
A few bits short of a byte.
A few bits shy of a word.
A few bricks shy of a load.
A few cans short of a six pack, six short.
A few clowns short of a circus.
A few clues shy of a solution.
A few ears short of a bushel.
A few eggs short of a dozen.
A few feet short of the runway.
A few fish short of a string.
A few guppies short of an aquarium.
A few inches short of a foot / yard.
A few kernels short of an ear.
A few lanes short of a highway.
A few lines short of a program.
A few links shy of a chain.
A few open splices.
A few peas short of a pod / casserole.
A few pickles short of a jar.
A few pixels short of an image.
A few puppies short of a pet shop.
A few rungs short of a ladder.
A few sandwiches short of a picnic.
A few screams short of an orgasm.
A few screws loose.
A few snowballs short of an avalanche.
A few spoons short of a full set.
A few straws shy of a bale.
A few tacos short of a fiesta platter.
A few tiles missing from his Space Shuttle.
A few tomatoes short of a thick sauce.
A few yards short of the hole.
A flower short of an arrangement.
A goose short of a gaggle.
A hamburger short of a Happy Meal.
A pane short of a window.
A pickle short of a barrel.
A room temperature IQ.
A strawberry short of a quart.
A teabag short of a pot.
A victim of retroactive birth control.
A violin minus the bow.
A walking argument for birth control.
A wind-up clock without a key.
About a half a bubble off plumb.
About as sharp as a sack a bowling ball .
About as smart as bait.
All booster - no payload.
All booster and no shuttle.
All crown - no filling.
All foam. no beer.
All hammer, no nail.
All his eggs in the same basket.
All his marbles in one bag.
All lime and salt, no tequila.
All missile, no warhead.
All plow and no tractor.
All wax and no wick.
Almost as smart as a finch.
Always in the right place, but at the wrong time.
Always sharpening his sleeping skills.
An early example of the Peter Principle.
An ego like a black hole.
An experiment in Artificial Stupidity.
An inch short and a stroke early.
An intellect rivaled only by garden tools.
Answers the door when the phone rings.
Antenna doesn't pick up all the channels.
Any slower and he'd be in reverse. -- Gignac
As thick as two short planks.
Attention span of an overripe grapefruit.
Attic's a little dusty.
Back burners not fully operating.
Bats have flown the belfry, and now he's all alone.
Bats in the belfry.
Batteries not included.
Been playing in the pharmacy section again.
Been playing with his wand too much.
Been short on oxygen one time too many.
Blender doesn't go past "mix".
Blocked one too many hockey pucks / soccer balls / punches.
Body by Fisher - Brains by Mattel.
Born a day late and like that ever since.
Born during low tide in the gene pool.
Brain on cruise control.
Brains of a house plant.
Bright as Alaska in December.
Broadcasts static.
Caboose seems to be pulling the engine.
Cackles a lot, but I ain't seen no eggs yet.
Can be outwitted by a jar of Marshmallow Fluff.
Can carry on conversations with bushes.
Can easily be confused with facts.
Car's only got three wheels, and one's going flat.
Cheezwiz for brains.
Cheats when filling out opinion polls.
Chimney's clogged.
Clutch is slipping.
Could get lost in a broom closet.
Couldn't hit sand if he fell off a camel.
Couldn't pick the winner of a one-horse race.
Crazy as all get out / a loon.
Cursor's flashing but there's no response.
Deaf, dumb, and blonde.
Deck has no face cards.
Diagonally parked in a parallel universe.
Dialing thumb must be broken.
Dock doesn't quite reach the water.
Does aerobics... in his head.
Doesn’t have all nine players on the diamond.
Doesn't have all his dogs barking.
Doesn't have all of his groceries in the same bag.
Doesn't have all the dots on his dice.
Doesn't have both oars in the water.
Doesn't have elastic in both of his socks.
Doesn't have his belt through all the loops.
Doesn't know if he's afoot or on horseback.
Driving with two wheels in the sand.
Dumber than owl droppings.
Eating with only one chopstick.
Echoes between the ears.
Elevator doesn't go all the way to the top floor.
Elevator doesn't make it to the penthouse.
Elevator doesn't stop at every floor.
Elevator is stuck between floors.
Encyclopaedia’s missing some volumes.
Engine is running, but no one is behind the wheel.
Evidence for the theory of a missing link.
Flying / landing on one engine.
Forgot to pay his brain bill.
Found his marbles, but is playing jacks with them.
Full throttle, dry tank.
Gasoline engine, diesel fuel.
Gavel doesn't quite hit the bench.
Gets her mail at an unknown zip code.
Gets his orders from another planet.
Goalie for the dart team.
God might still use him for miracle practice.
God's favorite target for lightning strikes.
Got a dozen eggs but some are cracked.
Got a life, but wasn't sure what to do with it.
Half a brick short of a full load.
Half a quart low.
Hard to distinguish from the tail end of a horse.
Has a leak in his ceiling.
Has a pulse, but that's about all.
Has all the brains God gave a duck's ass.
Has the brains of a dog’s ass.
Has the intellectual capacity of an Allen wrench.
Has the memory of a goldfish.
Hasn't enough sense to pound salt into a rat hole.
Hasn't got all his china in the cupboard.
Hasn't got the brains God gave a cat.
Having a party in his head, but no one else is invited.
Head whistles in a cross wind.
Hears everything that a dog can.
His drill doesn't have a full set of bits.
If there were a merciful God he'd be dead by now.
Immune to caffeine and all other stimulants.
Impervious to brain damage.
In the shopping mall of the mind, he's in the toy department.
Infinite space between her ears.
Informationally deprived.
Inspired the slogan, "A mind is a terrible thing to waste."
Intellectually challenged.
Knitting with only one needle.
Knows Atlanta like the back of her hand, but she’s in Chicago.
Lamborghini chassis, moped engine.
Left the store without all of his groceries.
Light not burning too bright.
Lightbulb over his head is burned out.
Lights are on but nobody's home.
Like a one-armed man climbing a rope.
Little red choo-choo done jumped the track.
Lives in the same world, but a different universe.
Living proof of evolution.
Long on dry wall, short on studs.
Looking for a nickel in the corner of a circular room.
Loony as a jay bird.
Lost his trolleys.
Low on thinking gas.
Marching to a different kettle of fish.
Mental agility of a soap dish.
Mentally qualified for handicapped parking.
Mercifully free of the ravages of intelligence.
Mind is on vacation but his mouth is working overtime.
Mind like a steel trap -- full of mice.
Mind like a steel trap -- rusty and stuck closed.
Mind like a steel trap -- things wander in and get mangled.
Mind wandered and never came back.
Missing a few buttons on his remote control.
Missing a few catalog cards / gears / marbles.
Missing a layer of insulation in his attic.
Missing all of the face cards.
Mouth is in gear, brain is in neutral.
Moves his lips to pretend he's reading.
Needs another brain to make half-wit.
Needs both hands to wipe his behind.
No coins in the old fountain.
No filter in the coffee maker.
No grain in the silo.
No hands on the rudder / yoke.
No hay in the loft.
No one at the throttle.
No wind in her mind's windmills.
Not digging in the same ditch with the rest of us!
Not done evolving yet.
Not enough brain cells for the Prozac to be effective.
Not enough brains to get anywhere near the gutter.
Not enough sense to come in out of the rain.
Not firing on all four / six / eight cylinders.
Not firing on all thrusters.
Not much to show for four billion years of evolution.
Not only rude, but ugly too.
Not quite human any longer.
Not running on full thrusters.
Not the brightest light on the Christmas tree.
Not the fastest car in the lot.
Not the quickest bunny in the forest.
Not the same since they took him off his medication.
Not the sharpest crayon in the box.
Not the sharpest knife in the drawer.
Not too tightly wrapped.
Nothing between the stethoscopes.
Nutty as a fruitcake.
Off his rocker.
Oil doesn't reach his dipstick
A couple of bricks short of a hod.
A couple of knights short of a Crusade.
A couple of togas short of an orgy.
A couple of volts below threshold.
A couplet short of a sonnet.
A day late and a dollar short.
A few beers short of a six-pack.
A few birds shy of a flock.
A few bits short of a byte.
A few bits shy of a word.
A few bricks shy of a load.
A few cans short of a six pack, six short.
A few clowns short of a circus.
A few clues shy of a solution.
A few ears short of a bushel.
A few eggs short of a dozen.
A few feet short of the runway.
A few fish short of a string.
A few guppies short of an aquarium.
A few inches short of a foot / yard.
A few kernels short of an ear.
A few lanes short of a highway.
A few lines short of a program.
A few links shy of a chain.
A few open splices.
A few peas short of a pod / casserole.
A few pickles short of a jar.
A few pixels short of an image.
A few puppies short of a pet shop.
A few rungs short of a ladder.
A few sandwiches short of a picnic.
A few screams short of an orgasm.
A few screws loose.
A few snowballs short of an avalanche.
A few spoons short of a full set.
A few straws shy of a bale.
A few tacos short of a fiesta platter.
A few tiles missing from his Space Shuttle.
A few tomatoes short of a thick sauce.
A few yards short of the hole.
A flower short of an arrangement.
A goose short of a gaggle.
A hamburger short of a Happy Meal.
A pane short of a window.
A pickle short of a barrel.
A room temperature IQ.
A strawberry short of a quart.
A teabag short of a pot.
A victim of retroactive birth control.
A violin minus the bow.
A walking argument for birth control.
A wind-up clock without a key.
About a half a bubble off plumb.
About as sharp as a sack a bowling ball .
About as smart as bait.
All booster - no payload.
All booster and no shuttle.
All crown - no filling.
All foam. no beer.
All hammer, no nail.
All his eggs in the same basket.
All his marbles in one bag.
All lime and salt, no tequila.
All missile, no warhead.
All plow and no tractor.
All wax and no wick.
Almost as smart as a finch.
Always in the right place, but at the wrong time.
Always sharpening his sleeping skills.
An early example of the Peter Principle.
An ego like a black hole.
An experiment in Artificial Stupidity.
An inch short and a stroke early.
An intellect rivaled only by garden tools.
Answers the door when the phone rings.
Antenna doesn't pick up all the channels.
Any slower and he'd be in reverse. -- Gignac
As thick as two short planks.
Attention span of an overripe grapefruit.
Attic's a little dusty.
Back burners not fully operating.
Bats have flown the belfry, and now he's all alone.
Bats in the belfry.
Batteries not included.
Been playing in the pharmacy section again.
Been playing with his wand too much.
Been short on oxygen one time too many.
Blender doesn't go past "mix".
Blocked one too many hockey pucks / soccer balls / punches.
Body by Fisher - Brains by Mattel.
Born a day late and like that ever since.
Born during low tide in the gene pool.
Brain on cruise control.
Brains of a house plant.
Bright as Alaska in December.
Broadcasts static.
Caboose seems to be pulling the engine.
Cackles a lot, but I ain't seen no eggs yet.
Can be outwitted by a jar of Marshmallow Fluff.
Can carry on conversations with bushes.
Can easily be confused with facts.
Car's only got three wheels, and one's going flat.
Cheezwiz for brains.
Cheats when filling out opinion polls.
Chimney's clogged.
Clutch is slipping.
Could get lost in a broom closet.
Couldn't hit sand if he fell off a camel.
Couldn't pick the winner of a one-horse race.
Crazy as all get out / a loon.
Cursor's flashing but there's no response.
Deaf, dumb, and blonde.
Deck has no face cards.
Diagonally parked in a parallel universe.
Dialing thumb must be broken.
Dock doesn't quite reach the water.
Does aerobics... in his head.
Doesn’t have all nine players on the diamond.
Doesn't have all his dogs barking.
Doesn't have all of his groceries in the same bag.
Doesn't have all the dots on his dice.
Doesn't have both oars in the water.
Doesn't have elastic in both of his socks.
Doesn't have his belt through all the loops.
Doesn't know if he's afoot or on horseback.
Driving with two wheels in the sand.
Dumber than owl droppings.
Eating with only one chopstick.
Echoes between the ears.
Elevator doesn't go all the way to the top floor.
Elevator doesn't make it to the penthouse.
Elevator doesn't stop at every floor.
Elevator is stuck between floors.
Encyclopaedia’s missing some volumes.
Engine is running, but no one is behind the wheel.
Evidence for the theory of a missing link.
Flying / landing on one engine.
Forgot to pay his brain bill.
Found his marbles, but is playing jacks with them.
Full throttle, dry tank.
Gasoline engine, diesel fuel.
Gavel doesn't quite hit the bench.
Gets her mail at an unknown zip code.
Gets his orders from another planet.
Goalie for the dart team.
God might still use him for miracle practice.
God's favorite target for lightning strikes.
Got a dozen eggs but some are cracked.
Got a life, but wasn't sure what to do with it.
Half a brick short of a full load.
Half a quart low.
Hard to distinguish from the tail end of a horse.
Has a leak in his ceiling.
Has a pulse, but that's about all.
Has all the brains God gave a duck's ass.
Has the brains of a dog’s ass.
Has the intellectual capacity of an Allen wrench.
Has the memory of a goldfish.
Hasn't enough sense to pound salt into a rat hole.
Hasn't got all his china in the cupboard.
Hasn't got the brains God gave a cat.
Having a party in his head, but no one else is invited.
Head whistles in a cross wind.
Hears everything that a dog can.
His drill doesn't have a full set of bits.
If there were a merciful God he'd be dead by now.
Immune to caffeine and all other stimulants.
Impervious to brain damage.
In the shopping mall of the mind, he's in the toy department.
Infinite space between her ears.
Informationally deprived.
Inspired the slogan, "A mind is a terrible thing to waste."
Intellectually challenged.
Knitting with only one needle.
Knows Atlanta like the back of her hand, but she’s in Chicago.
Lamborghini chassis, moped engine.
Left the store without all of his groceries.
Light not burning too bright.
Lightbulb over his head is burned out.
Lights are on but nobody's home.
Like a one-armed man climbing a rope.
Little red choo-choo done jumped the track.
Lives in the same world, but a different universe.
Living proof of evolution.
Long on dry wall, short on studs.
Looking for a nickel in the corner of a circular room.
Loony as a jay bird.
Lost his trolleys.
Low on thinking gas.
Marching to a different kettle of fish.
Mental agility of a soap dish.
Mentally qualified for handicapped parking.
Mercifully free of the ravages of intelligence.
Mind is on vacation but his mouth is working overtime.
Mind like a steel trap -- full of mice.
Mind like a steel trap -- rusty and stuck closed.
Mind like a steel trap -- things wander in and get mangled.
Mind wandered and never came back.
Missing a few buttons on his remote control.
Missing a few catalog cards / gears / marbles.
Missing a layer of insulation in his attic.
Missing all of the face cards.
Mouth is in gear, brain is in neutral.
Moves his lips to pretend he's reading.
Needs another brain to make half-wit.
Needs both hands to wipe his behind.
No coins in the old fountain.
No filter in the coffee maker.
No grain in the silo.
No hands on the rudder / yoke.
No hay in the loft.
No one at the throttle.
No wind in her mind's windmills.
Not digging in the same ditch with the rest of us!
Not done evolving yet.
Not enough brain cells for the Prozac to be effective.
Not enough brains to get anywhere near the gutter.
Not enough sense to come in out of the rain.
Not firing on all four / six / eight cylinders.
Not firing on all thrusters.
Not much to show for four billion years of evolution.
Not only rude, but ugly too.
Not quite human any longer.
Not running on full thrusters.
Not the brightest light on the Christmas tree.
Not the fastest car in the lot.
Not the quickest bunny in the forest.
Not the same since they took him off his medication.
Not the sharpest crayon in the box.
Not the sharpest knife in the drawer.
Not too tightly wrapped.
Nothing between the stethoscopes.
Nutty as a fruitcake.
Off his rocker.
Oil doesn't reach his dipstick