…aka falling on the grenade.

A man who is performing the wingman duty is obligated to entertain the designated ugly or fat friend (DUFF) of the girl his buddy is trying to score with.

This duty can range anywhere from buying a drink to leaving the bar with her.

Should one thing lead to another, and the wingman ends up hooking up with the DUFF, an immediate vow of silence is understood and the wingman shall never hear of it again.