spoilsport
noun

- a person who stops other people from enjoying themselves

(Cambridge Dictionary)
    
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ORIGIN

The word spoil has various meanings, but it has been used in the sense of "destroy" from the mid-1500s.

And the word sport comes from Middle English verb sporten. It can be defined as an activity that requires physical skill, and is commonly performed as a contest.

Because sport is enjoyable, referring to someone who ruins the fun for others as a "spoilsport" seems to come from the children's book "How the Grinch Stole Christmas" by Dr Seuss. You can also call this type of person a grinch.

Here are some more expressions that use the word "sport":

- a good sport = someone who plays fair and remains pleasant despite a loss (Roger didn't get recognition for the project, but he's being a good sport about it)

- a poor sport = someone who blames others for their failure (Jim won't talk to me because he claims I stole his customer. What a poor sport!)

- a sporting chance = a fair opportunity (Poor Penelope. She didn't have a sporting chance of reaching her sales target last year)


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SYNONYMS

pessimistic person, killjoy, grinch, sourpuss, drag, downer, malcontent, stick in the mud, party pooper, wet blanket

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Practice OWAD in a conversation:

"Oh come on Jim, don't be such a SPOILSPORT! You can't leave the party after only 20 minutes!"