Pin the Tail on the Donkey is a game

Game

A game is structured playing, usually undertaken for enjoyment and sometimes used as an educational tool. Games are distinct from work, which is usually carried out for remuneration, and from art, which is more often an expression of aesthetic or ideological elements...

 played by groups of children. It is common at birthday parties and other gatherings. A picture of a donkey

Donkey

The donkey or ass, Equus africanus asinus, is a domesticated member of the Equidae or horse family. The wild ancestor of the donkey is the African Wild Ass, E...

 with a missing tail is tacked to a wall within easy reach of children.
One at a time, each child is blindfold

Blindfold

A blindfold is a garment, usually of cloth, tied to one's head to cover the eyes to disable the wearer's sight. It can be worn when the eyes are in a closed state and thus prevents the wearer from opening them...

ed and handed a paper "tail" with a push pin or thumbtack poked through it. The blindfolded child is then spun around until he or she is disoriented. The child gropes around and tries to pin the tail on the donkey. The player who pins their tail closest to the target, the donkey's rear, wins. The game, a group

Group (sociology)

In the social sciences a social group can be defined as two or more humans who interact with one another, share similar characteristics and collectively have a sense of unity...

 activity, is generally not competitive; "winning" is only of marginal importance.

The game is also used in child development research.

The game can also be played by teenagers and adults, especially if the "donkey" is replaced with depictions of something or someone else. As a drinking game

Drinking game

Drinking games are games which involve the consumption of alcoholic beverages. These games vary widely in scope and complexity, although the purpose of most is to become intoxicated as quickly as possible...

, the person with the worst tail pinning is awarded one shot of a selected alcohol, to be determined by house rules or the loser in a friendly environment.

Idiomatically, the term can be used derisively for any assigned activity which is pointless or for which a person has been handicapped (blindfolded).