Marzocchi Star Fork (their first one). I installed the fork, pressed down on it, and the air valve / cap ejected from the fork and hit me in the face.
Answer Manitou (the first 'post Bradbury' fork). At least this stayed on my bike but it flexed more than it went up and down.
Flexstem - I went to bunnyhop a log, and the area behind the elastomer snapped, sending me flying over the bar.
Specialized M2 Team Ed frame. Only 500 made, made from the same stuff as bits of the Space Shuttle (with hindsight maybe not the greatest of brags....), and super strong. In around 5 months I'd cracked it behind the head tube, bent the top tube, knocked the rear triangle out of line, and all the paint fell off.
Tioga Farm John tire. Dear God..... Proves that pros will endorse any old shit for money. That stayed on my bike for one ride.
3T alloy bar. It would ben every other ride, so I'd just remove it, turn it upside down and re-install it! I guess it deserves some credit for not snapping.....
I could probably keep typing all morning :D