booby prize
From Longman Dictionary of Contemporary Englishbooby prizeˈbooby prize noun [countable] informal LASTa prize given as a joke to the person who is last in a competitionExamples from the Corpusbooby prize• It could only be because she thought they'd win a kind of booby prize.• If they were giving out prizes for what you do in bed he'd have come away with the booby prize.