Unfortunately, this is not TMI. (I wish. It would mean I'd had sex sometime this year.) No, I appear to have done it biting my nails. I don't remember the actual injuring, but as the motion needed to bite my nails set off my 'paaaaaaaaaaaain' reaction, it's a fair assumption.
As I have also recently chipped one of my front teeth biting my nails, this is probably an indication that I should really Stop That.
The problem, of course, it's that I have evolved nail biting into a tic that is so bad I can't let my nails grow out AT ALL or I'll rip them off at the roots. This means cutting them practically every day to the absolute quick, and I STILL manage to rip them off occasionally, which is why I have a dreadfully sore index finger right now as well. I also gnaw at my cuticles if the nails aren't available, and I really have no idea how to just MAKE IT STOP. I'm pretty sure it's actually compulsive now, which means I have to fight that much harder because I barely notice I'm doing it half the time and am probably doing it as a stress relief of some sort as well.