Killjoy noun
A person who stops other people from enjoying themselves or having fun.
I don't want to be a killjoy, but we will have an exam tomorrow morning.
Mary is called a killjoy just because she often refuses to drink alcohol in a party
The plural form of "killjoy" is "killjoys".
The noun dates from 1776.
Daughter: So I really want all my friends to have a great time. I was thinking it would be a good idea to have some candy out on the tables for people to snack on.
Mother: Well, if you want them to really enjoy themselves, candy is dandy but liquor is quicker.