When your boyfriend has cheated on you, you get your friend to seduce and sleep with them for revenge. It doesn't logically work, but your friend gets to feel better about themselves and, if said friend is homosexual, your ex-boyfriend starts to feel very confused about himself and therefore you feel much better.
Person 1: I know he cheated on you, but he is really cute. If you want i can have revenge sex with him for you.
Person 2: ????
Revenge sex occurs when a person's significant other cheats on them. The person who was cheated on then through some means (usually facebook) finds out who the "other woman/man's" most recent ex was. The person then hunts down said ex and has sex with that person to get revenge on the cheaters.
Julian: Hey remember that big fat blob i was dating and cheated on?
Rick: yeah i remember
Julian: she had revenge sex with the other chick's ex-boyfriend!
Rick: got any smokes?
Sex that occurs as a direct result of a nymphomaniacal need for sex after a fight or other type of malicious behavior. Also linked to makeup sex, makeup sex as a result of a pre-planned fight or argument, and angry sex.
This one time me and my girl were fighting so bad that the cops showed up. After we cooled down for a few hours we met back at my place to talk and she was wicked pissed. At the tend she let me know that she was over it as soon as she got home and the whole thing was a set-up to get her some revenge sex. It was the tits.