I was born two months early, and had to have surgery to take out part of my small intestine. The result is a long scar across my abdomen, and whenever I show it to people they think it's badass (the scar and nice abs make a nice combo). When people ask I usually tell them one of these three stories:
1. I had a scuffle with a rhino
2. I was in a knife fight
3. I was pregnant and had to get a c-section
It's great when I can actually convince people on one of my stories. Just for kicks, I once convinced my little sister that she gave me my scar by scratching me, and made her feel pretty guilty about it for a few days. It was pretty funny.