This anecdote was circulating on teh interwebs. I doubt its actual veracity, but I nevertheless found it compellingly funny.
(I'm waiting in line behind a woman speaking on her cellphone in another language. Ahead of me is a white man. After the woman hangs up, he speaks up.)
Man: "I didn't want to say anything while you were on the phone, but you're in America now. You need to speak English."
Woman: "Excuse me?"
Man: *very slow* "If you want to speak Mexican, go back to Mexico. In America, we speak English."
Woman: "Sir, I was speaking Navajo. If you want to speak English, go back to England."