There was another occasion these days, but maybe your sister missed it — Jay Leno had been joking with Scarlett Johansson about her filming in Bulgaria (and not in Rome, as she was supposed to).

I do not mind the jokes, but I don't like when they are made with ignorance. Especially when Bulgarians are mistaken with Russians, this can make me angry sometimes ;-)

Bulgarians are not innocent too — they also like to joke with nations and peoples that they do not know anything about, just based on prejudices and stereotypes - like white South Africans (for being racist), Albanians (for being extremely backward), Chukcha (a small people, living on the Far East edge of Russia, just in front of Alaska, for being mentally challenged). Everything in brackets is a Bulgarian prejudice, not the truth! So it's the same anywhere in the world, just the scale is different and more noticeable in the USA.

And the probability that someone will sue you over a Bulgarian joke is quite low in the USA, when a Polish or a Jewish joke can be expensive, nowadays.