I have a few.
First, in grade 4 or something like that, I was with a couple of friends in an open, two-level log cabin type thing on the playground. I was on the second level, which was about 6 feet off the ground, laughing at something or other with my back to the edge of the second level floor (which had no guard rail of any sort). I was laughing so hard that I stepped backwards and failed to realize the balls of my feet no longer had anything solid under them, so down I went, backwards, not unlike a felled tree. For some reason, I remember quite clearly that that my last words were, “Hahahaha – aaAAAAH!” The back of my head landed on the 4x4 beam that served as the base for the entrance to the cabin. I ran around the playground holding my head and whining “Ow, ow, ow, ow!” Well, it did hurt. A lot. I had a nice big knot on my head, but no lasting damage, thankfully. Now give back me shillelagh!
Then, when I was about 10 or 11, I was getting up off my bed from a seated position when I completely failed my negotiations with gravity and fell into the corner of a night table with my forehead. Head wounds bleed an awful lot, even though the size of the cut turned out not to be all that huge. It did leave a scar though, right in the center at the hairline. My head took a beating when I was a kid. Ostrich!
About five or six years ago, the wife and I were moving my computer desk into another room, when I learned an important lesson: Remove all movable objects from a heavy piece of furniture before attempting to move it. This lesson was taught to me by the keyboard drawer as it slid out and landed corner-first on my big toe from a height of about three feet. Lost my toenail and couldn’t walk properly for three weeks.
Then, three years ago at my previous job, I was booking in some tools for repair. This one was still in its tool case, which was held closed with a plastic zip tie to prevent it from opening in transit. So I grab the toolbox and steady it with my right hand, then take a box cutter to it with my left (I’m a lefty). Upon unexpectedly cutting through the last bit of tie sooner than I’d thought, Newton’s first law did what it’s best at, such that the object in motion (the box cutter) stayed in motion until acted upon by an unbalanced force (the index finger of my right hand). Right up to the hilt, enough that the tip was poking out the other side. Not fun, but I’m thankful box cutters only have short blades. It was a good time to do it though, as the crew from a fire truck were shopping in the store part of the building at the time, so they had some gauze and disinfectant on hand, patched me up well enough to live.