I bite my fingernails, too. My middle fingers are absolutely disgusting and I can't get them to grow into a decent fingernail. I just heard that biting your fingernails leads to having pinworms or something, though. Y'know, the worms that live in your ass and come out at night. That's just disgusting. I'm pretty sure I'll stop biting my fingernails now so I don't have to think about little white worms crawling around my asshole at night.