spoilsport

American  

[spoil-spawrt, -spohrt] / ˈspɔɪlˌspɔrt, -ˌspoʊrt /

noun

1. a person whose selfish or unsportsmanlike attitudes or actions spoil the pleasure of others, as in a game or social gathering.

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spoilsport British  

/ ˈspɔɪlˌspɔːt /

noun

1. informal a person who spoils the pleasure of other people by his actions or attitudes

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Etymology

Origin of spoilsport

First recorded in 1815–25; from phrase spoil the sport

Explanation

A spoilsport is a person who ruins other people's fun. You know: the girl shushing everyone at a sleepover party, the kid who refuses to play when it comes their turn to be "it." Back before it meant organized athletics, sport meant games or joking. Instead of making fun of someone, you'd be "making sport" of them. So someone who spoils or wrecks the fun or sport of others is a spoilsport. Calling someone a spoilsport, though, is often just a way to pressure them to do something everyone knows is wrong.

Example Sentences

Spoilsport that he is, Cellan-Jones then went on the web and discovered that "Mr Vanjoki had made the same claim in a blog back in July".

From The Guardian • Sep. 18, 2010