>>6
that's bullshit. That may be a definition in a dictionary, but that's not what people mean by "nice guy", when describing a guy who doesn't get girls.
Yes, nice guys do have personality traits like "not aggressive", but rather than try to define the traits of a nice guy, let us try to determine the symptoms of being a nice guy. You are a nice guy if...
1) you have a lot of difficulty getting a gf, or laid. Particularly telling of a nice guy is if he whines that he can't get a gf. The more he whines, and the more self pity he has, the more of a nice guy he is.
2) you prefer the company of female friends opposed to men. However, your female friends are not attracted to you. If your girlfriends tell you that you deserve a gf, but they will not be your girlfriend, you are a nice guy.
3) you are afraid to be yourself around girls because 1) you are shy, or 2) you fear they will think you are a bastard. ie: you are afraid to ask girls out, afraid to kiss them, afraid to say anything controversial around girls you like.
4) you think that being overly nice to girls will make them like you. ie: doing them favours whenever they ask without question. Buying them shit like flowers, or writing poetry about them.