booby prize

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. An award given to the one who performs worst in a game or contest.
2. n. Informal Acknowledgment of great inferiority, as in ability.

Century Dictionary and Cyclopedia

1. n. See prize.

Wiktionary

1. n. idiomatic A prize or status, often unwelcome, awarded as a joke or disincentive to the loser of a contest or for poor performance.

GNU Webster's 1913

1. n. an award for the poorest performance in a competition; hence, metaphorically, the recognition of a strikingly inferior or incompetent performance.

WordNet 3.0

1. n. a prize given to one who finishes last in a contest