A "Nice Guy (TM)" is a man who thinks being a basic human being with a brain, means he should receive sex or something romantic from her. Basically just a horny asshole.
Nice Guys post stuff like "If you sucked a man's dick like you suck in your stomach, maybe you could keep a man." or, "When you finally meet a man who has goals, isn't full of himself and asks you out at 12 pm not 12 am, 'I like you as a friend.' ". They complain about not having a girl and how girls are "all the same".
Nice guys will talk to a girl who just got broken up with and be all "You're so pretty" "I love your figure" blah blah blah but as soon as the girl says no, they go full psycho mode. They go on this crazy insult rampage being all "I was just offering a mercy fuck" this, and "Ur so ugly. Fat pig. I never even liked you anyways. All girls are the same". They're assholes who switch their moods when they're rejected. Adult babies. They throw tantrums when they don't get what they want. Not a person you wanna be. Anyways, hope this educated you and answered your questions.
See Jimmy over there? Yeah he's a Nice Guy.