On Xbox live, I cant even talk without an american automatically making fun of me.
Whenever that happens I just a cheesy phrase like "i am rubber you are glue" and always be sure to make them get the impression that you dont care what they think about you, as you dont care about them, and its always good to have them leave the lobby thinking "im a jerk" to themselves. Dont keep at it, if you just simply correct them and dont even insult them for being stupid and judging you by a stereotype, then ignore them and they wont gain another victim that they can argue with/ insult. A lot of the people of XBL just want to put others down because they dont have a life.