Have to put in my two cents :)
In Spain, I met this girl once who simply would not listen to me when I told her Americans do not eat hamburgers every night. "I know someone who went," she'd tell me. "Maybe YOU don't eat hamburgers every night, but everyone else in America does." It was surreal.
In Greece this summer, I used to pretend I was from Canada... There was all this graffitti all over Athens that said U-swatstika-A, which was kind of disturbing. Greece was really against our involvement in Kosovo, which I was too, so there -- but it was easier to get things for cheap when I said, Emay apo teen Canada :)
I guess so far as jokes go, nothing bothers me. But outright ignorance and hatred does.
Loretta