Hi.
Yuck. Some people are very stupid and ignorant. I know this doesn't help that much but it is true. This whole thing is about the fact that these people:
1. don't know much about any culture (and aren't interested in learning),
2. are idiots
3. are insensitive (see #1).
Racial stereotypes are super annoying and wrong. I think people from every background or experience have some time in their lives when people misunderstand things about them, make fun of them and refuse to take the time to understand them.
Understanding -- not being sympathetic to, but realizing the shortcomings of -- these people who instantly stereotype and judge is important because you just feel sorry for them in the end. In a way, all this can be empowering, because it's clear how ignorant and uncultured these people who tease you are. So it's not hard to triumph over them, even though it might be frustrating that your victories have to come silently, to yourself. That does take lots of confidence. But engaging with these kind of people is pretty useless; nothing smart is going to be said, and you'll just wind up becoming more frustrated. Also, sometimes, not responding can be the best way to get people to stop bothering you -- after all, people do it mainly to see that they're emotionally powerful over others.