I am quite accident-prone. Mostly I hot glue myself to things which I tend to do so well that the pain lingers for a few days. I also spear myself unmercifully with sewing needles, even dull embroidery ones, to the point where sometimes I draw blood.
I was so absorbed in a painting that I accidentally painted a blue spot on the side of my head when I scratched it with the wrong end of the brush.
The most memorable incident and the most painful was in middle school though. I didn't have a proper desk lamp, so I stripped the shade off a table lamp to have more light. I reached over the top of it to grab something, and my forearm touched the bulb which had been on for more than an hour. It was so hot that I couldn't feel the pain for a few seconds and I seared a perfectly round 2" spot onto my dominant arm. It turned a dark purplish-brown color and made it nearly impossible to do anything right-handed for over a month. It managed to heal completely though and I don't have even the tiniest sign of it now.