I’ve had my share. I did forget to tighten lug nuts on a friend’s car after checking the brakes and they lost a wheel.
I think my stupidest mistake was the time at a wrecking yard and I was pulling an LSD to put in my BMW and I didn’t have a support. I was lazily using my hand under the pumpkin to prevent it from falling. The last bolt came out and the pumpkin dropped to the ground, with my hand underneath it and a sliver of aluminum was driven in to my ring finger. I had to have it surgically removed.