Head of Vecna
The Head of Vecna was a hoax started by an epic troll named Mark Steuer. During a session, he decided that he was going to play a prank on some of the players, so he had some of them (Group One) set up a trap for the rest (Group Two).
The Head was claimed to be the severed head of the arch-lich (and later god of undeath) Vecna. Like the Hand and Eye of Vecna, the Head was said to give the wielder incredible power over the undead. Also like the Hand and Eye, the Head was a replacement for the wielder's own body part. Members of Group One playing NPCs spread the rumor, while the rest set up a crude temple full of weak traps to guard it. However, a n00b Drood who came in late found the head before the other group, buggered off into the woods, and summoned an ape to cut off his head and replace it. He checked it for magical properties, and found none - then did it anyway. His fail was epic.
Group Two finally caught up after hearing about the item. Once they arrived at the location of the Head, they began arguing over who would get to be decapitated. After a few rounds of in-game fighting, one of them managed to win over the group and get his stupid gourd lopped off. One of the other players started protesting, but the Head of Vecna was placed on the ragged neck stump of the wizard that won the argument.
Then, predictably, it just rolled off.
Group Two decided they had waited too long because of the argument, and cut the next guy's head off. The replaced it quickly, and... it fell off again.
It was at this time that Mark decided it was to funny not to laugh and told them about it. The Head of Vecna was just some poor jerk's severed head, and there was no magic - which they could have figured out if they had paid attention. And, of course, HE got blamed for the whole thing.
Case in point: read your source books.