I was talking with a shaman of my acquaintance today about a player we both know who regularly mutilates the English language beyond any reasonable explanation. "I need a bar for him, like I have for experience," the shaman said. "Every letter that he destroys will be one point on the bar, with five for extra stupidity, like every time he says a drop is "knise." When he gets to 100 points, I'm going to let him die in an instance by not healing him. Then the bar will start over again."
Healers have an exceptional capability to get revenge on other players, particularly on overzealous DPSers. The healers of my guild joke about a "blacklist" for hunters, rogues, mages and warlocks who anger them -- if you're on the blacklist, you get to die to AOE or your own aggro pulling until the healers feel you've suffered enough. They don't actually have the blacklist ... I think.
I've also seen a guild's druids band together to let a rogue die in every raid after he complained about a feral druid rolling on DPS gear in a 5-man instance because "druids are only good for healing." And many raid leaders who have been too rough yelling at their healers in Blackwing Lair have died due to coordinated priest heals on the Nefarian class call.
Most of the people that healers let die seem to have brought their own fate upon them, whether by recklessness ("I can totally solo that"), malice ("God, our healers really suck tonight") or other forms of stupidity. As Robert Heinlein said, "Stupidity is the only universal capital crime; the sentence is death, there is no appeal, and execution is carried out automatically and without pity" -- especially when you tick off the guys who hold your life in their hands. If you let them live, they'll never learn.
Healers, have you ever let someone die because they offended you or did something dumb? Or have you been the victim of a healing blacklist/intentional death?