booby prize

from The American Heritage® Dictionary of the English Language, 5th Edition.

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

from The Century Dictionary.

• noun See prize.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

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

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a prize given to one who finishes last in a contest