I gave a buddy a grip plug for his glock. I was installing it for him and it was pretty tight so I flipped the gun over and while trying to get leverage, my thumb hit the trigger.... with the muzzle pressed into my chest. Thank God there was only a click. I had NOT checked the gun, but it was empty. To this day, I don't think he or my wife know it happened.
As soon as I felt that click, my stomach was in knots.
You really should have put the safety on first.