The worst thing I have done, was 13 years ago. I just bought a reloader, and was checking the bullet depth on my revolver, to see if it cyclced ok. Click, click, maybe another. Ok. Opened the cylinder to find a live round mixed in. Luckily I observed the rule that you don't point guns at people, so it was pointed at the ceiling, above my bed. That could have really sucked.
Every now and then I pick up a gun, and do something that bothers me, like puttin my finger on the trigger. Which seems to be the more common one. Tonight I was going to clean my derringer, and I almost cocked it, and then realized, dumbass it is loaded. I didn't cock it, but just putting my thumb on the hammer bothered me. I hope the guilt about these things makes me a better gun owner.
Dammit, I just love cocking guns.
I have a buddy retired army, who discharged a loaded gun twice. One a 30-06 in a motel room. Kids were jumping on the bed, making all kinds of noise. He said after that, they sat down. No called the cops, he turned himeself in. Another one a hole in the camp floor with his 9mm. I can see how that could happen with semi autos, sorta.