Three things come to mind.
First is the warning they put on every box of plastic wrap. "Warning! Serrated cutting edge, be careful!" And every time I read that I think "Who on earth would be dumb enough to cut themselves on a box of wrap?" I lost count of how many times I've cut myself on it.
The second... I was taking some sheet pans out of an oven. This particular oven was the masterfully designed kind where both doors close in unison. If you push the left door shut, the right door shuts. You know what I'm talking about. I hate these. Anyway... In tight quarters, a new guy tries to move behind me on my left as I'm taking out a sheet pan and moving it to my right. He didn't realize that pushing the left door made the right door move. It caused me to smack a 400 degree sheet pan right into my neck. As much as I don't care about scars on my arms or hands, a scar on my face is another story. It took a lot of explaining to the owner why I hadn't shaved for the following two weeks. Thankfully it healed up without a scar.
Third, my restaurant was built in the 40's. The basement has a lot of the storage. There are a lot of low pipes and such. I'm in the habit of ducking, but when I was new there, I was walking to a cooler with a mixing bowl of flour. For no reason other than to entertain myself, I was flipping it around. Not paying attention to where I was going, I walked right into a low hanging pipe and completely floored myself and covered myself in flour. I still remember the impact of the back of my head against the concrete as I fell backwards as if Tyson just punched me in the face, and still marvel that it didn't really hurt. I must have laid on the ground for 5 minutes before I had the wherewithal to gather myself up and keep on going. Oddly enough, I didn't feel that bad afterwards, but those 5 minutes really sucked, and I had a couple lumps on my head for a good while.
Honorable mention... Once at a job we were remodelling one of the dining rooms which included large glass panes, probably four feet by four feet. A couple guys and I were carrying the panes out of the dining room and into storage, which involved an outside trip. On the last pane of the trip, the guy was walking outside carrying the pane and it suddenly just shattered. It was one of the strangest things I've ever seen. He stood there with a blank face and a piece of glass in each hand. After a few moments, he dropped the pieces but still had a blank stare. I asked him if he was alright. Turns out he was fine, but I'll never forget the guy's stare when the glass just shattered for some inexplicable reason. He didn't get hurt a bit, which was the most amazing part of all of it.