Nice Guys (TM) are the guys that make a point of announcing themselves as "nice", and who whine about never getting laid.
Many of the other definitions were written by "Nice Guys".
They think they're entitled to sex just because they hold open a door once in a while. They're unsure of themselves to the point they can't manage a declarative sentence. They think strumming guitar makes them deep and they can't understand why it hasn't turned them into a pussy magnet. They are, almost without fail, sexist but tell themselves they're not because, of course, they're a Nice Guy. They tell themselves "nice guys don't get ahead" as an excuse for their own failings. They wrongly believe that women only like jerks, and are deeply bitter about it.
Most women do not like jerks. Women really do like nice guys. But a nice guy is NOT the dude playing gentleman so he can be rewarded with head. The real nice guys -the ones women really do want to date and fuck -are the ones who are genuinely decent human beings. Guys who make a point of calling themselves Nice Guys do not generally fall under this category. And they wonder why they aren't getting any ladies?
So, you fucking internet whiners, how about instead of pissing and moaning about how women never see what a great fella you are and take your pants off all because you took them shopping (you charmer, you!) you actually put some effort into being a real, live nice person instead of a Nice Guy (TM) ?
"Man, ladies only like jerks! I totally took this smokin' hot piece of ass -er, I mean, young lady -out for coffee that one time and didn't even suggest she skip the whipped cream so she could keep from getting fat, and she STILL would rather go out with the dude that treats her like a human being! Nice guys just finish last, I guess."