Being a nice person isn’t bad but “nice guy” is a term for someone who presents themselves as nice and polite (but only to people they’re attracted to) and expects romantic attention in return for being nice. Basically, they think the fact that they put so much effort into being nice they deserve that romantic attention. They’ll often talk about how nice they are.
Of course, anyone who needs to repeatedly tell you they are nice tend not be.
Modern civilisation is slowly falling to barbarians, except none of the barbarians are foreigners.