spoilsport 

A person who ruins the fun for others. A buzzkill. This shitty person is to be avoided at all times.

Jane: Did u see how much she was yelling?
Ann: Yeah, what a spoilsport. She ruined the whole party.

spoilsport by Juliantchr August 31, 2021

spoil sport 

A person who ruins the fun or the enthusiasm of others.

"Come on, let's go to your cousin's party tonight and have some fun!"
"No, it won't be fun, and my cousin is NOT cute"
"Aw, don't be such a spoil sport!"

spoil sport by sosso March 15, 2009

spoilersport 

noun. One who destructively reveals plotlines or other details of a movie, story or book, simply for the sake of revealing a spoiler, or ruining a surprise ending for fans.

"Did you hear about who is in the coffin on the season finale of 'Lost?'"

"You should stop reading blogs written by spoilersports."

spoilersport by MoJoe13 June 18, 2008