I don't injure myself very often, but when I do, it's usually something really stupid.
In 4th grade my parents took my (10th grade) sister, her friend and me to a haunted house in a neighborhood strip mall. At the end of the haunted house, one of the goblins chased us out. Having been holding on to my sister's friend's coat, I let go and ran eye-first into a metal beam (holding up the over-hang outside the store). Blood gushed, my sister clasped her hands over my eye (blocking any path I had to see) and led me around the parking lot until we found our parents. Seven stitches later, I went home, just 6 days before my uncles wedding (which I was a junior bridesmaid in, luckily no black eye).
A couple of weeks later, I slipped on some ice during recess and cracked my head open. No stitches.
As a sophomore in high school, I was warming up before a hockey game. I knew the door to the ice was open. I didn't realize, while skating backwards, that I was next to the door. I tripped, hitting my neck on the rough corner of the plexi door. My neck looked like raw hamburger - mottled purple and red, and swollen. I could barely turn my head. I only missed one shift of the game, but looked like someone had thrown me down a set of stairs for about a week afterward.
Also in high school, a friend had a plate slip out of her hand as she was taking it out of the cupboard, it hit just below my eye, slicing down to the bone.
A couple of years ago I was making cupcakes for my birthday party. Being in a hurry (and maybe a little lazy), I tried to use a ceramic bowl on my stand mixer (as the stainless steal bowl was already in use). Well, the bowl (of course) broke, spun, and when I tried to grab it, sliced my right hand. The cut wasn't very big, but somewhat deep and in a precarious spot... on my palm, near my thumb. I drove myself to urgent care for 2 stitches. Then had to drag my lidocained-hand to the grocery store for more supplies to finish the cupcakes (which were delicious!). Cooking, mousing, typing, and general every-day stuff is tough to accomplish without your right-hand thumb.
Then last night, as I was warming into my racketball game (losing 8-0), I swung, completely missed the ball and squarely struck my left hand. Instantly my left ring finger had a purple line hashed across the tip, the red-purple color was spreading. I shook my hand, danced around with watering eyes and continuously said "OWE, owE, Owe." The tingling spread across my three main fingers, and I was afraid to move them. I couldn't help but laugh at the ridiculous injury. After some ice, I managed to slowly bend each finger, determining they weren't broken. All night they tingled like crazy. Today I have a seriously bruised finger tip (which makes typing, well, interesting).