Spoilsport

A spoilsport is a person who ruins other people's fun.

Don't be a spoilsport.

"I know it is sudden, but this is your client, King Harkinian of Hyrule." "So this is the King I'm defending. I've never defended royalty before..!" "LOL I LEARNED TO TEXT WITH MY MOUTH. WHAT DO YOU THINK?" "I KNOW it isn't funny." "...Spoilsport."

Don't be such a spoilsport.

Altan doesn't miss a single chance to be a spoilsport.

Don't be a spoilsport!

I know I am a sad spoilsport, but it would make me wretched.

He looks a spoilsport. There are men in whose presence it is impossible to have any fun: men who are a sort of walking conscience.

It may seem somewhat spoilsport to focus in on this negative after another important victory but to ignore it would be delusion. Southgate will not be letting it escape his attention.