I agree with the others. You could say something like "I've had enough" and just get up and walk away -- or say nothing at all. Some people are just plain stupid and continually making someone the brunt of their dopey jokes is just plain rude. I don't think they would like it if they were on the other end of it.

I'm sorry this happens to you. It shouldn't happen to anyone. God bless and please take care of YOU. Hugs, Lee