Okay, so this isn't an exploit. It's still damn funny, and I can't think of a better place to put it.
If you go to the Sanctum in Quel'danas, PvP flag yourself and stand on the Blood Elf quest-giver. The resulting action is that most of the opposite faction that try to talk to the Blood Elf will, instead, auto-attack you and be completely screwed over.
While their subsequent grief reports will possibly attract a GM, the GM will basically just tell you to move. I estimate that in a half hour of watching television, I killed at least 100 Alliance without ever actually attacking anyone.
It gives you a laugh, AND it helps the economy by creating a gold sink! Everybody wins!