I have a problem.
When i talk to an English-speaking person, and can't hear a word or a sentence he says, i ask him: "What?"
It's terribly impolite. It sounds very "Israeli". In English one should say "Excuse me?" or "I beg your pardon?..", even when talking to friends -- and i say "What?" when talking to people i don't know. Every time i do it, i regret it the moment after, but just can't rid myself of it. I should try to do better when i'm in London Town.