Rain on somebody's parade - Idioms by The Free Dictionary
rain on somebody's parade
rain on (one's) parade
To ruin one's plans or temper one's excitement. I hate to rain on your parade, but I think your A in chemistry was actually a clerical error. Mom really rained on our parade by chaperoning our school dance.
ˌrain on somebody’s ˈparade (American English) spoil something for somebody: Drugs again rained on the Olympics’ parade as another athlete tested positive for an illegal substance.