1. Expression of a fucked up situation, such as, but not limited to:
Popping it in the "wrong" hole
your best friend cheating on your with your fiance (Not from personal exp. but I'm sure that would suck).
2. A word meaning "Dammit".
Guy 1: "Hey man, think I could get some spare change?"
Guy 2: "Grrfuck dude, I spent my last bit of cash on this chick I met the other day."