OK, Seriously

[CaptainBubba]

My theory:

If you are nice to a girl, she'll feel as if she deserves better. Since we are all lustful bastards at heart, better=sexier.

Sexy guys are mean because they never had to be nice to get girls.

Because he is mean they feel as if they couldn't do better. (KEEP IN MIND BETTER=SEXIER)

If a girl meets a nice guy who is also sexy, then of course shell go for him. They're pretty damn rare though, and most guys are just latent assholes who beleive they're just nice but misunderstood guys.