1) Forgot to fully tighten lug nuts when rotating Mom's tires. One wheel came off while she was driving and passed her on the road when she slowed down.

2) Borrowed friend's Dad's Buick for a trip from NY to Virginia Beach. Smart enough to check the oil on the way back. Dumb enough to not fully close the hood when I finished.

The hood tried to stay back in Virginia Beach when I hit 65mph leaving town.

Both happened when I was 17 (many years ago).

I still keep my wrenching to a minimum if possible.