Taking the seat off makes it a whole new experience.
Anyways, we're right up in my area of expertise here. As soon as I learned to ride a bike (which came from about 15 minutes of getting shoved into the bushes by my first girlfriend's older brothers) I never wore any protective equipment, so I've got a shitload of scars.
1: When I was around 10, I decided to try riding down a large flight of stairs for the first time. Being the stupid little kid I was, I picked a steep series of stairs and had too much speed going into em. I flew right over the first 5 or so steps, then came tumbling down the rest of the stairs. Total injuries: Quarter sized cut on my left knee, dime sized cut on my right elbow, bruises, minor scrapes.
2: I got my first BMX bike for my 12th birthday. I used to live in a place called Rock Island, and it had hills pretty much everywhere. My favorite one was in a park right by my house. It had a road that snaked back and forth down it, and benches at each turn. About halfway down one time, my brake cable snapped, and I flew right into a bench. Total injuries: wide impact wound in my right calf (bench corner), cracked rib, bruises all up my right arm.
3: At an indoor skatepark, I was going up a ramp, and my shoe slipped off and flew over the ramp. I skidded backwards, with my bike laying on top of me. My shoe hit a skater going up the other side of the ramp, and he flew over and hit my bike. Total injuries: cracked sternum, minor cuncussion.
4: Different skatepark, I was learning to ride a vert ramp. I freaked out going up it, dropped my bike, and tried to land on the ramp. I missed, and caught my stomach along the edge of the roll in. I have a scar across my bellybutton. It's right over the line you get across your stomach when you're sitting and leaning forward for too long. Fortunately it wasn't deep enough to need scars. Total injuries: Near disembowelment, bruised knee.
5: Downhill racing, my chain came off. Total injuries: removed most skin on my left knee, quarter sized cut on my right knee, scrapes covering both forearms.
6: Riding on a funbox, my tire blew out, and I twisted my right ankle all the way behind me, turning inside. It literally swelled up to the size of an ostrich egg. Total injuries: Major sprain.
7: A friend kicked a skateboard in front of my wheel, and I flipped over the handlebars, landing on my pavement. To make matters worse, it was blacktop, during summer, covered with rocks, and I wasn't wearing a shirt. Total injuries: scrapes covering my back, pavement induced wedgie.
The following happened to one of my friends.
8: Racing down a hill, my friend's wheels skidded while turning into our neighborhood. He hit the curb going sideways and flew into a wall. He hit near the corner, so the wall gave him no leeway. Total injuries: deep gashes on his left elbow, deep scrapes on his right forearm, cuts covering both palms.
9: Riding a slanted wall, his wheel locked up and his handlebars came loose. He fell 8 feet onto his face, and dislocated his shoulders. He can now clap his elbows. Literally clap them. To put it in perspective, hook your thumbs into your belt loops, put your hands in your pockets, and try to clap your elbows together. Even better? He's semi-fat. Total injuries: Minor cuts, dislocated shoulders.