Never had one but had three close calls.
First time, I was "inspecting" a friend's new Beretta 92F. I had a S&W 4006 with the mag. safety; hence my coming assumption.
I dropped the mag on the Beretta and proceeded to pull the trigger to check its feel, but about 2/3 of the way home, something, I don't know what, told me to check the chamber. Lo and behold was one in the pipe.
I had the piece pointed at my leg. Just about crapped on that one after I realized what had almost happened.
The second time was after I got a 70s series 1911. I put one in the pipe and for some reason decided to drop the hammer by pinching it with my thumb and index finger. It slipped and fell pretty hard. I almost crapped when I saw a very distinct dent in the primer! Pure luck. That one was pointed at the wall in a downward direction--I learned a little from the first time.
Third time, I just got an SKS. I was in my bedroom. I was ignorant of letting the bolt fly forward on a round in the chamber (can you say slam fire?). When I ejected the round, again, a prominent dent in the primer. Later on, at the range, that very rifle did indeed go full auto when I let the bolt slam too hard on a round in the chamber. That made the bedroom boo-boo seem worse. I sold that rifle.
These were all in my early 20s when I was more prone to exiciteability and lack of care. I'm much more calm these days and make a conscious effort to observe the basic rules.