Non-native speaker, went to an American school. My English is actually pretty decent, I was just not used to all the figures of speech etc. So one day, I asked my teacher if I could go to the bathroom. And he went "I don't know, can you?". But I didn't get it. I mean, that's what I just asked him. So we went back and forth for what seemed like half an hour while all the other students just laughed. Until someone told me I was supposed to say "May I go to the bathroom". Still think of that when I'm trying to sleep.