Not quite the same, but here's my favorite "DOH!" moment:

After fixing the left door lock mechanism (which I had broken previously), I had everything put back together nice and tidy. Then I had to immediately remove the door panels to figure out what I had broken this time. Obviously I had shorted something out because the passenger window wouldn't roll down. Yep... only after removing the panels did I instantly remember the window lock button - I must have accidentally pressed it.

Fortunately it's really not my fault though since... well, uh, something, something, something...