I was in college and bought a blank dagger blade from a nearby knife shop I used as a letter opener/throwing knife. One night, bored while waiting around for a date, I started to throw the blade into a cheap wooden stool in my living room. After an ambitious throw, the blade got stuck. I decided to wrench downward on the tang with my right hand while bracing the stool with my left hand. After one hard tug I got the blade free but dragged the tip of the dagger across the top of my left hand - right where the base of my thumb meets the palm. I distinctly recall feeling the tip bounce off my thumb bone, then looking down to see a neat cross section of skin, ligament and bone. I marveled at how little it hurt until blood literally squirted at a 45 degree angle onto the wall five feet in front of me. I sprinted to the kitchen to find a towel to start applying pressure and, finding none, ran across the house to the bathroom where I frantically grabbed any gauze/cotton patches I could find. It would not stop gushing.
I finally managed to twist a hand towel around my hand tight enough to stem the bleeding (I could tell the bleeding started to slow when the red patch on the towel stopped growing). Feeling light-headed, I sat down in the living room and kept pressure on my hand for a few minutes. Not long after that, my roommate returned with his girlfriend who shrieked when he turned on the hall light and noticed blood splattered on the wall, trailing into the kitchen, then back towards the bathroom/bedrooms. They soon noticed me on the couch, asked who had been murdered in our house, and were incredulous when I said I had "merely nicked myself." I quickly called my girlfriend to cancel our plans - feigning a sudden bout of food poisoning, as I knew she would force me to go to an emergency clinic for stitches. She nearly throttled me the next day when she saw my homemade bandage made from cotton rounds and duct tape.
Luckily the blade missed the ligaments and the wound sealed up nicely. It was the worst injury I've inflicted on myself so far. I probably should have gone to a doctor for that one...