I do it when I'm defending myself and I did it when I just wanna be an ass.
That doesn't necessarily make you a bully HO, just defending yourself.
It may be that you are just winding them up, due to how they are with you. If you are antagonized, then you need your defence to get you through.
Bullying is for example - unprovoked words, nasty remarks with spiteful undertones to them as well as physical bullying.
As long as you don't then turn into them, you will be OK.