On an old server we had an event in Gurubashi Arena called 'Kill the GM.'
Self explanatory, any PvP resulted in kick and a ban from the event.
The rewards were leet, exclusive winner's tabard (Tabard of Fire/Frost but with added stats), Rings, Winner's trinket, Winner's neck, and a winner's cape.
It was a good event. Whoever got the killing blow got to choose from one of those items.