A couple of things come to mind. Nothing really happened with either, but I can't think of anything worse:
First, years ago, when I was active duty army as a 15B Aircraft Powerplant Repairer (in the guard now), I was clipping blades on the first stage of the compressor due to damage. There's 20 blades in the first stage, and you have to clip the one opposite as well to maintain balance. Well, I counted wrong and clipped the wrong blade. The GE rep (representative from General Electric, who makes the engine) was right there and must not have been paying attention. It ended fine, though, just extra work I had to do.
Second, less years ago at my current job as a Diesel Technician, I was doing a warranty repair for a service bulletin. I was still pretty new here, and warranty jobs pay less time, but this was like the third one I had done and was making good time, so I was trying to hurry. It was cold that day, and people complain when you have the bay doors open, so I had it just open enough to raise the cab, which meant the door was almost all the way open anyway. When I had done as much as I could do with the truck in the shop, I lowered the cab so I could pull it out and use our forklift to remove the part. I had forgotten about the door and ran into it. Didn't get in any trouble though, just had to take a drug test per policy, and the door doesn't close right to this day.