Either ignore him or show him how much of an idiot he's being.
I don't recommend this at all, but I'd find something he enjoys, look up the negative stereotypes, and use the info to send the crap he does right back at him. I know that's stooping to his level, but I'd like to give him a taste of his own crappy medicine. But again, I am not recommending that, I'm just saying. ._.;;