A fag has lots of ways that makes him into a fag, like a bag holding many differentthings.
Dude, that guy has an I heart Justin Bieber shirt, dresses his dog like a bunny, and puts pictures of shirtless men on Facebook. He is a total fag bag.
A friend or acquaintance than is being a total loser and not wanting to do anything cool and would rather go to bed at a normal time instead of staying up late getting hammered and kissing fat chicks.