FMJ

Foul Mouthed Jerk - a now-legendary term from a disgruntled poster on an automotive internet forum, to a group of fellow posters he took offence to. The other posters turned it into a humourous term for someone they liked. Originally used in a derogatory fashion, it is now used to denote yourself as someone you're proud to be (like a rebel) and you wear it on t-shirts and greet other FMJs with it. There is even a racing team devoted to the term and it was probably not the original poster's intentions to make it as big as it has become.