What women are referring to when they talk about a 'nice guy'? It means a guy who:
Is confident around women.
Is confident around other guys.
Knows how to behave like a 'challenge'.
Takes on the masculine role in an interaction, on a date or in a relationship.
Respects women, but also gives plenty of time and attention to his life and what he's achieving/trying to achieve.
Uses humor in an attractive way and Confidently makes conversation in an interesting way with women.
It is not a bad thing to be a nice guys just not a "push over". Hopes this helps clear up the nice guy thing.