spoiled sport 

Petty, spiteful complaining after losing a sporting event.

The spoiled sports pummeled our mascot after we won the big game.

spoiled sport by RKeller1 April 19, 2010

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