Painful.
However, Bodyboarder is 100% correct: It's the internal vanes that determine which way the disc goes, not the grooves. Some discs ARE grooved forwards to clear the pad better at the expense of wear, most are grooved backwards though. Thing is, you can't tell just from looking at the side, end of.
But yeah, great way to ingratiate yourself onto a new forum. Nothing like a bit of aggression, eh? Bet you're a riot when you walk into a new pub and start picking a fight with the locals.