The mind game, often brought up unintentionally by your friends, where you begin comparing yourself to your boyfriend or girlfriend's ex. Often occurs when someone says something about you that is extremely similar to the ex or a trait completely opposite of you that you're jealous of.
Guy 1: My girlfriend and I got into fight cause she was texting her ex tonight, what's he got that I don't?
Guy 2: Dude, don't play the comparison game, you'll probably lose.
Girl 1: Oh, him and his ex-girlfriend used to always make sushi together, too!
Girl 2: Thanks for starting another round of the comparison game, bitch.