Funny, I pay zero attention to other guys' hands or nails. Totally unaware of it. I only notice when they have their fingers in their mouths, which as I said in the previous post looks like hell. It really is a terrible habit and sends an extremely negative message to people who see you doing this.
Its kinda like bad posture, a weak handshake, a mousy voice, not making eye contact, etc. Its very bad body language. It sends a negative vibe out. Those who do it are probably unaware that they are doing it. But believe me those around you who see you are quite aware and take you down a few notches in respect.