I'm going to bust on myself, here are a couple of the dumb things I've done:

I was installing foglights on my car once,
the drill slipped and I hit the condensor and I was showered with freon.
It was so thick I couldn't see the car.
Scared the heck out of me, I didn't know what I hit at first.

I drilled into my gas tank once.
It was near the top so it was an easy add a screw fix.

I'm sure there is more.