boner-killer

noun2

1. •
   (slang, vulgar) Something that causes loss of libido and thus of an erection.

   • “And honestly? I don't want to talk about this with you. Not now. This is like the biggest boner killer I could think of.” — 2014
2. •
   (disapproving, vulgar) An unappealing person or situation.

   • That was a pretty sweet movie, but the ending was a real boner-killer.