Saw a guy in football hyperextend his knee. Basically, he was running a 5 yard out, and got his knee taken out by a guy trying to tackle him. The knee bent backwards. Almost 75 degrees (from the videos we saw afterwards). And there was a loud *SNAP* then a sucking noise and a *POP*. And I was about 25 yards away from this.
There was one time when I was mowing the lawn at my parents' house and I went to dump the grass in the compost pile. Well, as I stepped back there I stepped on a nail. It went through the sole of my shoe, through my foot, and out the top. It was the weirdest feeling. It didn't hurt going in, but I kind of felt something slide between the bones in my foot. Then I looked down, realized what had happened and pulled my foot off of the board with the nail in it. I looked around for more boards with nails in them, grabbed the one I had stepped on, and then shattered it when I threw it against the garage. It started to throb at that point and I pulled my shoe and sock off and there was blood everywhere. I even had a little pool of it in my shoe (kind of like when you get water in your shoe and it sloshes around). I told my dad what happened and we went to the doctor's office for a tetanus shot and to see if it needed stitches. No stitches were needed.
Even better than that was this wrestling meet I was at. This one guy kept getting beat by a better skilled opponent (points wise and technique wise). So the one guy shot in, grappled with the other, got the other guy in a head and arm, and decided to squeeze, pull down a bit, and out (I knew how to do this too). And out popped the other guy's arm from his shoulder. It was pretty nasty, and it pissed a bunch of us off (on my team) because that's not how to really win. We really gave that guy some dirty looks on the bus ride back to the school. It kind of made a sucking sound, then a loud pop, and the other guy was crying.
I did that to a guy once as well, though it was by accident, and not nearly as bad. He got his arm caught when I rolled him over and pinned him. It kind of popped out a bit (I could see the end of the upper arm bone, and his collar bone was flexed at a weird angle), but it didn't come all the way out. And there were plenty of times in wrestling when I hyper-extended my elbows. That hurt a hell of a lot.