buzzkill

(noun) a person who spoils other peoples’ fun by being very boring

Example Sentences:

A: Let’s go to the beach! I want to sit in the sun! It’s been a long winter!
B: I don’t want to get skin cancer.
A: Okay, let’s go get a beer!
B: Beer makes you fat.
A: Do you want to go shopping?
B: I don’t want to spend money.
A: You are such a buzzkill.

Every time Stuart and his friends go out for dinner, he makes them feel bad about eating expensive food because poor people can’t afford to eat it. Stuart is a buzzkill.

Wayne: Let’s go clubbing! I want to get drunk!
Garth: I’d rather stay home and drink milk.
Wayne: You are a buzzkill.

From the Blogs:

Sorry to be the buzzkill