T'est fou, la. Flit mon tu. (local Shaques for "you are crazy, bite me"... toned down a touch in translation... actually it's to do with somebody named Richard and no actual biting unless you are French and are gentle).

As has been stated, there really is no way that I know of to tell someone to "fuck off" in French. There are international signs of friendship but these are sans voice and require no translation. Although they may differ somewhat between cultures, there is little problem with recognition. The NA version being "the finger". The European versin is not as static and uses two fingers, sometimes an entire forearm but the Europeons are naturally kinda passionate and sometimes a bit more kinky in these matters.