Typically a scenario when there are two couples on a date and a fifth 'wheel' joins the group. While the couples carry on and keep the daterolling forward, the fifth wheel sits on the back of the group and gives no real contribution to the progression of the evening.
Guy #1: Dude, why was Mike so pissed all night when we went out?
Guy #2: He was just annoyed that he was jeeping with us the whole time.