#1 to #3: Rode my bike into the back of a parked car. Why #1 to #3? Broken nose, 2 broken teeth.
#4: Building my first bike, running the front der cable over the wrong cable guide under the BB shell.
#5: Getting the little nipple gizmos that let you put a Presta tube in a Schrader wheel, putting on the new rim tape, remounting the tire & tube, starting to inflate the tube when I noticed said gizmos still sitting on the work bench.
#6: Cutting the brake cable on my road bike getting ready to replace it (I didn't want to drag the ragged end through my fairly new housing) and then discovering I had picked up MTB brake cables and of course LBS was then closed.

If I wasn't stupid, I wouldn't have any claim to fame. (By the way, as a non-pro I regard mounting tires with the labels on the non-drive side as just a way to get a cleaner looking bike. In the same vein, when we flatten bikes for shipping at Bikes-not-Bombs we alway put the pedals on the inside of the cranks, so I might have thought that was deliberate.)