I once accidentally ran at an open window, and it knocked me over. Didn't get knocked out, but I did have a triangular hole in my forehead for awhile.
My brother managed to smack his head into a bookcase whilst getting changed. Has a small scar on his head... not sure what came off worse - the bookcase or him ¬¬.
Edit: above post reminds me something silly my partner did. He had some beer bottles in the boot of my car, and one smashed. He decided to try and sort it, despite my protests at the side of the road. Ended up cutting his thumb, so I ended up driving the last 1-2min home lol ><. Should've kept driving like I told him.