when two people in a relationship opt to hang out with only each other instead of joining friends or engaging in other social activity. the decision to "couple out" is consciously made by each member in the relationship, under the acknowledgment of the possible consequences: (1) never being invited to hang out with friends ever again , (2) losing one's reputation of being fun-loving and/or cool, (3) the risk of being verbally shamed by terms like "pussy whipped" or "lame" when seen again by friends.
Brett: "Why isn't our boy here at our party?"
Chet: "I just called him. Him and his girl are going to couple-out. They're going to watch a movie at home instead."
Brett: "Lame, dude."