I'm such a nice guy.

A typical saying by guys who's not generally nice. They're simply saying this thinking the girls will have sex with them if they say this phrase. They generally say this over and over to a girl, so she thinks he's a nice guy, but once she rejects him his true colors come to the surface.

Fake Nice Guy: "I'm such a nice guy. Why won't these bitches have sex with me?"
An Actual Nice Guy: "Girls won't have sex with you, because you're a total douchebag."
Fake Nice Guy: "Whatever asshole, I am a nice guy. Girls are just total bitches!"
An Actual Nice Guy: "Whatever helps you sleep at night."