Defeat Johnson? Why? They say, he's a party pooper

• Wet blanket
• (informal) someone who spoils the pleasure of others

Longman Dictionary of Contemporary English Word definitions in Longman Dictionary of Contemporary English
noun EXAMPLES FROM OTHER ENTRIES ▪ We wanted to do a sponsored dance after work but those killjoys in Head Office wouldn't let us.

Wiktionary Word definitions in Wiktionary
n. A person who is anti-fun, or prevents others from having fun

Wikipedia Word definitions in Wikipedia
Killjoy is a horror film franchise which focuses on the titular Killjoy, a demonic clown who is summoned to assist revenge plots in all three films, only to prove too overwhelming for each character who calls him. Produced by Full Moon Features , the series ...

Douglas Harper's Etymology Dictionary Word definitions in Douglas Harper's Etymology Dictionary
also kill-joy , 1776, from kill (v.) + joy . Formerly used with other stems (such as kill-courtesy "boorish person," kill-cow "bully, big man," etc.).