My scar isn't nearly as interesting as the story behind it. I have a roughly circular scar on my left knee about an inch and a half in diameter.
When I was in high school there was a railroad behind my house that lead out of town. It was rarely in use, but plenty of old railway cars were stored there, and they were all linked together. So obviously the best thing to do was climb them, and run along the top jumping from car to car. It was pretty fun, but some of the cars had a last rung bolted to the top of the walkway that stuck up into the air just enough to slip a foot under. Naturally my foot got hooked under one while making a landing, and I fell onto the metal walkway on top of the train car, which is very similar to a cheese grater. This took a large chunk out of my knee, and I could see a severed vein, which covered my entire lower leg in blood on during the walk home.
The aftermath is fun too. No serious injury, but I had to cut the hanging flesh from my leg with a knife. It hadn't been entirely torn off, and was connected by a thread of live skin.
The funny thing is at the time it didn't really bother me, but I get a little queasy thinking about it now.