Since everybody else is admitting screwups, I guess I'll join in. I've got two.
1. When I was about fifteen, I was climbing into a permanent treestand with my Revelation Model 200, (a Marlin 336 clone), with one in the pipe. Big no no. I was almost up to the top when I dropped it, straight down, butt first. It hit the ground with the barrel pointed straight up at me. Thank God for the lever action's half cock safety keeping the hammer off the firing pin.
2. A couple of years later, I had a Ruger MKII Target in my front pants pocket. I reached for it, and stupidly put my finger in the trigger gaurd. BANG! right in my pocket. I felt a burning sensation down my thigh and my heart nearly stopped from fear. I dropped my pants, expecting the worst, and was relieved to see only a three or four inch red line down the front of my leg.
These two instances were unexcusable and irresponsible. The good thing is, that both turned out much better than they could have, and they have made me the safety nut I am today. Now, I'm absolutely anal about it, to the point of pissing people off, but I don't care. I was given two freebies, and don't plan on tempting fate again.