OKay, this is how I racked myself when I was younger.
I was teaching myself to ride a two-wheeler in our driveway, but I took a turn too wide and ran full speed into our fence. I slid forward off the seat and landed on the bar in front of the seat. ouch.
Another time I was at my friend's house and we were riding near this creek with kinda steep walls. We decided it would be fun to ride down into the creek. He started going diagnally down the wall, but I though going straight down would be more fun. I started going really fast, and I managed to hit a rock about halfway down. I flew the rest of the way down (man that was so much fun) and landed on my back on a solid rock creek bottom, which knocked the wind outta me pretty good. I had to dive out of the way before my bike hit me. It missed me by like 3 inches.
And to finish off today's post, once I tried to make a little bike ramp in the street because I wanted to do a jump. I stacked up some bricks and put down a board of plywood. I went to the top of my street, faster and faster. I was hoping for some good air, which I got, but my bike wasn't with me. I scraped myself off the street to see what had happened. I had knocked off the plywood when I hit it and my tires got tangled up in the bricks. Probably of of my best flights distancewise.
Oh and guess what? I've never sprained or broken anything

I think that's why I'm so careless.