The opposite would be someone who is shitty, selfish, and totally square in the sack.
An internet meme appearing on 4chan, Reddit, and other sites about the classiest guy around. The meme involves a photo of a smiling, confident, stubbled guy smoking a joint and giving a friendly reassuring look toward the camera. On top of this photo, people will write of Good Guy Greg's classy deeds. He borrows your car and returns it with a full tank of gas. He parties with you on your birthday but never tells anyone about how you puked on yourself. He comes over for dinner and washes the dishes. He is better than you in every way, but never talks about it and makes you feel better about yourself instead.
Buyer: Hey man, do you have change for a second 20?
Dealer/GGG: Nah dude, just take it for 20.
Buyer: That guy's such a GGG!