I contemplated putting this on the exploit forum, but decided it was more appropriate to this one . . .
So I noticed (and judging by the comments I'm not the first one) that the Drowned Thunder Lizard's Tail (Drowned Thunder Lizard Tail - Item - World of Warcraft) stays in your inventory even after turning in the quest. It's from one of the new Fishing Dailys in Orgrimmar (not sure if Alliance can get anything similar).
Even better, it can be used *anywhere* and creates a cool blue smoke cloud with lightning effects for roughly 2 seconds. It's thick enough that at first, you can't even see the person inside of it.
I've macroed mine into Blink, and I've noticed that on more than one occasion players are left behind inspecting the blue cloud assuming I'm still inside of it because they don't actaully see me disappear. I contemplated putting this on the exploit forum, but decided it was more appropriate to this one . . .
At any rate, it's a really fun, though unintentional, toy.
Edit:
Small bummer in the newest hotfix notes:
Razgar’s Fillet Knife and Drowned Thunder Lizard Tail are now removed from a player’s inventory upon completing the quest “A Golden Opportunity” in Orgrimmar.
Still, I don't think this will prevent the item from being used if you already have it, or if you simply don't turn in the quest.