I knew that story (with soup insteand of cookies though) but t wanted to teach a complete different lesson: one about sharing, about realising that the ones that ask would give too, and they do. In the one I saw there was a white woman having lunch and standing up to go to the toilet (it was a video). When she comes back she sees a young black man drinking her soup. She does nothing but trying to take the spoon back to eat from it. He looks at her, smiles, and gives her another spoon. When she is ready to leave, still surprised and angry, she sees that she had seated in the wrong table and her soup was still on the table.
It was part of a programme to support inmigrants, refugess and fight racism.