Well, here in Bangkok we have a special situation. It is a cultural thing for Thai (and Chinese) men to have long fingernails. (I think it comes from old China where mandarins used to keep their nails long to show that they did not work with their hands, and thus show their status). There is nothing that could convince them to cut their nails short. The result: My hands and wrists look like geographical maps because of the engravings done by my partners. Of course there is a lot of blood involved (it's amazing how much a tiny nail scratch can bleed). I don't think someone could catch HIV this way, but I'm always afraid because of the open wounds. Now I refuse to practice with longnailed guys.
Curiously, ladies keep their nails short