'Add Your Own Fluff' D&D Cursed Item: The Fusing Longsword.

  Place this cursed longsword decorated with gold in a treasure pile, sit back and wait. This particular cursed item is cruel for two reasons. The obvious reason is that it's cursed, but the other one is that what triggers the curse is the next critical hit rolled by the player character wielding it!!!
  It will be all the more glorious when the player's initial joy at getting a critical hit is met by the DM with a "Roll a saving throw against..."! (Fortitude for 3.5 -you pick the DC-, Magical Device for old-school games, etc)
  If the player fails his roll, his hand(s) become(s) permanently fused to the sword! (To state the obvious, whether it's one hand or two depends on how the character was holding the sword.) Gauntlets or gloves will not stop this effect, in fact they will be fused along with the hands to the handle of the sword. And to clarify, one can't just cut the skin around the hand or nonsense like that; the sword doesn't become glued to affected hands, they merge together, bones and flesh magically melting around and into the sword handle.
  Even if the player manages his saving throw, once the curse has been initially triggered it will now require a new saving throw for every successful hit, no longer just with critical hits. Giving it to someone else will reset the trigger for that person, but not for anyone who triggered it before and uses it again.
  To be fair though, the character now cannot be disarmed of the sword, the fusing causes no damage since it's magical and the successful attacks that trigger the curse still take place normally otherwise. There's no reason to be mean to players. ;)