When you see a girl you like and you hook up with her without getting a good look at her friend. You proceed to call your wingman over to hook up with her friend. Then you realize you hooked your friend up with the better looking girl. Hence, the reverse wingman.
*after the hook up*
Elliot: "Man I hooked up with a hot chick last night"
K-Dub: "So did I. I appreciate being the wingman with a the better looking chick. I'm always cool with being the reverse wingman."
Somebody who preforms the reverse wingman must initially attempt to wing his friend. But after getting the girl warmed up and mentioning your friend, she has no desire to meet him, and takes interest in you. This is where she invites you back and you complete the move. Note: there should be little intent to get with the girl originally.
Guy1: "Hey buddy, can you wing me with that blonde over there?"
Reverse Wingman (RW): "Sure, bro, let me go warm her up and I'll wave you over."
*RW chats with blonde for too long*
Blonde: "So listen, how about we get out of her and you can stay at my place."
RW: "I mean I'm not gonna argue with you, lead the way"
Guy 1: *look of despair*
RW: *Not my fault look*
Guy1: (to himself) Damn what a perfect execution of the Reverse Wingman
The fat and/or ugly chick who accompanies the hottie at the bar, making it impossible to score with the hottie.
This operates as follows: by directing your attention at the hot chick who has a Reverse Wingman, you are implicitly offending the Reverse Wingman, thereby giving the hottie an excuse to condemn you as unfeeling, shallow, insensitive, looks-obsessed, etc. Hotties bring the Reverse Wingman along when they, the hotties, either genuinely wish to be left alone, or when they want to be a tease and derive sadistic pleasure from rebuffing all advances. Do not reward this behavior! Or even better, flirt with the Reverse Wingman...it'll drive the hottie crazy.