What is the most devastating Insult in your country?

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All we have heard about Bush and the shoes, don't we? That made me think about this issue: what is the most insulting thing or phrase you can (but shouldn't) do or say in your country? Here in Portugal calling "Filho da P***" (son of a wh*re) is a very insulting phrase, and sticking your third finger in the air is an obscene gesture. Please be polite, we don't know who is reading this, ok? LOL