(noun) Used to describe a person who conducts those social activities usually carried out by a group or a couple by himself, most often because his friends all have significant others. Extension of the term third wheel, which is usually used to describe the person who awkwardly tags along with their coupled-up friends. More generally, a Lone Banana is anyone who conducts certain social activities by himself. The term has a sad or lonely connotation. Derived from the single banana phenomenon often observed in grocery stores, when bananas that have become separated from the bunch are sold as singles.
He’s been kind of a Lone Banana ever since his buddy found a girlfriend.
Look at that Lone Banana out to dinner by himself. Maybe we should ask him to sit with us.