It’s very simple: if you have to say that you are a nice guy, you’re not.
Go read this article on Feministe
If a self-styled “Nice Guy” complains that the reason he can’t get laid is that women only like “jerks” who treat them badly, chances are he’s got a sense of entitlement on him the size of the Unisphere.
So Nice Guys® are the people who think that girls (that is, the girls they *deserve* to date, because those girls are 20 years younger than them and way out of their league) only date jerks. They come to this conclusion because they opened a door for a girl once and that didn’t immediately get them laid like it *should* have, because any basic human decency towards women has to be repaid by sex. Now.
I dated a Nice Guy® a couple years back. It was the worst thing I’ve ever put myself through. He said things to chip away at my self-worth (told me I needed to loose weight a lot, which was hilarious because he was much heavier than me) and threw honest to goodness temper tantrums whenever I said something critical or suggested that it was ok if I never made plans but he could at least pretend to ask me if I was okay with whatever he informed me we were doing that day. And threatened to kill himself if I left. (In a weird way, I’m glad, because it was the kick in the ass I apparently needed to build myself a self-esteem and start thinking I was worth something and that, no, I didn’t need to put up with shit from everyone, because if I did, this was exactly how bad my life was going to be).