I am the notorious master of, when late into raids, accidentally popping Heroism (the buff spell with a 10-minute timer) BEFORE a major boss fight.
The best stupid trick, though, was actually a MUD story rather than a MMO story. I only witnessed it, I didn’t do it.
I used to run a MUD with open, in-character PvP. There was an in-character Law Patrol, even, to enforce some standards of behavior. Anyway, we had this one guy who was a max-level (lv50) mage, whose personal joy in life was killing lowbies for his jollies and then killing the patrolmen who’d hunt him down. Racked up literally millions in gold coins worth of bounty on his head, but no one could nail him.
So finally, one night (I was on IC as the God of Law) I’d had enough–he was chain-killing people level 10 and under, and taunting about it on shout. I wasn’t going to break my own rules by smiting the guy unless absolutely necessary (for various politics reasons with the other admins, I didn’t want to open that can of worms), but I wanted him to lose at least once. So I announced across the MUD, with a booming voice in the sky, “I desire that the blight of <badguy> be removed from my world. If you but pray for the opportunity, I shall transport him to your location for you to make the attempt.”
And I get one response. From a level 31 cleric who was not particularly associated with Good/Law. “Transport him to me, I can do it.” We went back and forth a few times, with me reminding him how little chance he had, but he was so insistent that I did it.
And the message immediately pops up in the log, within a second or two, “<badguy> has been playerkilled by <cleric>!”
I’m literally openmouthed in astonishment so I teleport to the cleric myself to see what’s what.
I arrive, take 1hp damage from the Cleric’s fire aura, and instantly plummet 15 rooms straight down a mineshaft. That the cleric was hovering over with a levitate spell. Landed right next to the broken corpse of the PvPer, who had died of falling damage and one tick of fire damage. And who never, to my knowledge, logged in again.