From Longman Dictionary of Contemporary Englishparty pooperparty poop‧er /ˈpɑːti ˌpuːpə $ ˈpɑːrti ˌpuːpər/ noun [countable] informalSPOIL someone who spoils other people’s fun
Examples from the Corpus
party pooper• His economic theories, however, made him a party pooper.• The other was simply a party pooper. 