Well, one time when I was still a virgin I was going down on my gf on the living room floor. She was sitting on the floor with her back against the couch, so it was kind of an odd angle. We had talked before this day and had kind of decided that we would complete the deed this day, i.e. go all the way. So we were both pretty excited. Anyway, she started bucking pretty wildly and ended up smashing her pubic bone against my face so hard she gave me a bloody nose. It took an hour to get that thing to stop bleeding, so by that time, neither one of us was in the mood to finish up.
Then, while living in the dorms at college I had a lofted bed. There was only about 1.5 feet of clearance between the bed and the ceiling. My fiancee (now my wife) and I would get numerous cuts and scrapes from going at it in the bed. The ceiling was covered in that "popcorn" type stuff, so it really tore up the skin nicely. Also, at the dorm, I was feeling a little ill one week. My gf came over and she was pretty horny, so even though I was feeling a little ill, we still had sex. Well, about 45 minutes into the session, I passed out. I woke up a bit later and she was freaking out because she didn't know what happened. That night I passed out again and my roommate had to take me to the emergency room. There they found out that I had severe strep throat and that I was dehydrated to the point of near death. So my gf actually nearly killed me by nailing me. Heh heh heh. It is pretty funny looking back, but it was scarey at the time.