a buzz kill

buzzkill

Someone or something that makes people less happy, excited, or enthusiastic about some event or thing. Primarily heard in US. I was so excited to see the concert, but all the technical problems with the lights and sound were such buzzkills. I'm sorry to be a buzzkill, everyone, but we've received a number of complaints from neighbors about the noise, so we'll have to turn down the music.
Farlex Dictionary of Idioms.

a buzz kill

AMERICAN, INFORMAL
If a person or something that happens is a buzz kill, they spoil an event by making people less happy and excited. Sorry I've been a buzz kill tonight. They discovered his money had been stolen. Talk about a buzz kill.
See also: buzz, kill
Collins COBUILD Idioms Dictionary, 3rd ed.
See also:
  • buzzkill
  • be like a dog with two tails
  • like a dog with two tails
  • be going on (for) (something)
  • be going on something
  • be wild about (someone or something)
  • get (one's) rocks off on (something)
  • between two stools, one falls to the ground
  • get carried away with (someone or something)
  • be potty about (something)
References in periodicals archive
One recent weekend, I was a buzz kill victim twice.
Beware the Buzz Kill: you can avoid being either a victim or a perp