When I took the Cooper Extension Course in Houston back in 1982, a Houston PD LEO was over on the extreme right side of the firing line. Since back then they had to carry in a flapped holster he was using his duty rig to become proficient with it and the 1911. We are in the middle of an exercise when I hear, "I'm hit!" I look over and the LEO is going down holding his right calf. Uncle Jeff, ever the instructor, yells for the rest of to stay on target and ignore the wounded man, while he and the range officer took care of the cop. The poor guy got disconnected with the flap and got his finger on the trigger (Rule 2) before he cleared leather and shot himself in the calf. I would not have wanted to 'splain that to my captain!
On the more humerous (and dumber) side....
I once went hunting with my best friend, his father and his two idiot uncles. I was around 16 or 17. The three brothers were famous for pulling gags on each other. At the very least one of their caps was sure to get ventilated this day. One uncle had a 12 ga shell used for scaring off birds, the kind that shoots out a small explosive charge that detonates among the birds and scares them off from airports and the like. He slips it into my friend's father's shotgun. We came to a shallow water-filled ditch, and one brother steps across. Just as he does my friend's dad shoots in the water from about six feet away to splash him. His shotgun goes boom and the little explosive makes a small and unimpressive splash in the water. There it is in the ditch water and the fuze is burning with a sizzling sound. My friend's father goes, "What the s###?!" and leans over to investigate the strange little sizzling device in the ditch with predictable results.
One thing about that group, we learned how not to behave around guns.