I've had an ND and an AD. The ND was totally my fault, I got complacent and not paying attention at the clearing barrel when I was in Afghanistan.
But my AD... Scared the bejesus out of me. I had sent my 1911 out for a competition trigger job. Got it back and was trying it out at the range. About 70 rounds into it, I had a FTF. I look down and see that my hammer was only at half cock. Which, on a 1911 should never happen. It's either unchambered and hammer could be down but, the hammer is cocked if a round is in the chamber.
So I used my strong hand thumb to re-cock the hammer. Before I knew it, the hammer dropped and sent the round into the berm, put railroad tracks on my thumb, and the gun jumped out of my hand.
After I figured out what happened, I unloaded and cleared the weapon. I then duplicated the problem without ammo. Racking the side would leave the hammer at half cock, but using your thumb to cock it, it would drop all the way and fire the round, Took it back to my gunsmith who said "oh chit!!! It didn't go full auto on you did it?". He apologized and made it right.
Remember, ALWAYS keep it level and down range when handling!!
I did read on the net recently about a fellow who nearly shot his butt off when getting into his car. He had an old floppy leather holster, and it was do soft, floppy, that it folded into the trigger guard, then manipulated the trigger when he bent at the waist to get into his car.