I'm not entirely sure about my worst. I know I broke my finger once jumping up on the arm of a couch. I put my arms on it then jumped back, causing my finger to get caught on my pocket and be pushed all the way back till it just...snapped.
Another time I wrecked my bicycle. I brought it back on a wheelie, lost my balance and fell back, slamming my funny bone on a rock and it made a gash. Said gash bled so much that a white shirt I had was mostly red and after 4 or 5 washes it had to be thrown away. It bled for quite awhile, to, on an off for about a week. Didn't go to the doctor so I didn't get any stitches.
There was this other bike wreck, too. I was turning and hit some loose gravel and the bike fell over, I was going rather fast, so when I hit I just slid for about a foot or two. Wasn't too fat but it put a gash around where my kidney is, scraped my arm and knee up. It wasn't as bad as the first wreck, though.
The odd part is that the bike I had must have been cursed, since everyone who rode it had some really bad wreck.
There's this story my mom tells me about sometimes, though. Apparently, when I was little, I was jumping on a bean bag (No comment.) and fell head-first into one of those stone areas surrounding a fireplace. It apparently bled really bad and it caused a scar that's been on my forehead since then.
I've had a few more, but those were the worst of them all. As for which is the most worse, well, I can't decide.