Tycho has a great point here http://www.penny-arcade.com/2009/6/22/. This is something that creeps into every game, and must - at least once per campaign - be expunged with brutal ruthlessness.
Disintegrate one of the PC's favorite NPCs; Disjunction all their magic gear; or at least connive with one of your players to "take a fall" and have his character permanently killed and then replaced by a new PC. The player will be happy (because you let him make a great new character) and the rest of the group will be stricken with fear. Just make sure the player knows the cool new power you bribed him with stops working if the rest of the group ever finds out about the conspiracy.