The year was 1987 and the Mysantia game was in it's 6th year. The players were 5th Level(very high L for me around this time). The players were full of themselves because they were at the "lofty" level and loaded with magic items. I decided to knock them down a peg with a super organized, low level major threat: The Bloodbath Orcs.
The orcs all had 8 hp and were lead by a death knight , who was the equivalent of one of the 8 or so pcs. The orcs had crossbow orcs each with 2 females to reload. The warrior types slit the throats of unconscious PCs.
The PCs saw they were "only" fighting orcs, and underestimated them from the beginning, that is until the first throat got slit, then they panicked and proceeded to let the orcs decimate them .
The PC Mage was prob most responsible for the TPK, he was sloppy but most of all he had 2 scrolls., each of which was capable of ending the encounter in the parties favor but he refused to use them and his fireball was horribly used.
To this day the players remember this and say it was deliberate on my part, I admit it was a tough encounter. Ijust smile and remember the truth.
(Damn, Ive used my 3 posts for the day!)