put a damper on sth

put a damper on sth (to make smth less hopeful, cheerful, enjoyable, active, or great than it could have been etc; to have a dulling or numbing influence on something) — омрачать, портить что-либо (веселье, настроение, удовольствие т.д.); наводить тоску; ~ обломать кайф (разг.); воспрепятствовать, помешать чему-л.
Also put a dampener on sth

His glum mood /The rainy weather /The bad news /etc...
....(really / rather) put a damper on......
.......... their party
.......... on our picnic
.......... on everything.

Rain put a damper on our picnic plans.

Putting a damper on something makes it weaker. The expression is most often used when something diminishes or stops enthusiasm or excitement. The verb dampen, as in dampen enthusiasm, has the same meaning.

Example: Steve lost his wallet so that rather put a damper on the evening.
Example: We were both ill while we were in Boston, which put a bit of a dampener on things.
Example: A couple of knee injuries put a damper on his football career.
Example: I don't want to put a damper on anything for you but I will tell you about my experience.

More examples

Early Sunday morning, the storm hit North Carolina straight on and then spread northeast, causing slick roads and putting a damper on post-Christmas bargain-hunting. —Washington Post (12/27/2010)
I know it could put a damper on our relationship if I told him I loved him so soon. He may not feel the same way yet —Chicago Tribune (2/21/2012)
And even a more gradual decline in Europe could put a damper on the U.S. recovery. —The Washington Post (2/22/2012)

[rain on sb's parade]
[burst sb's bubble]
dampen one's spirit/enthusiasm

A damper is a type of a small movable plate/metal door in a stove, furnace, etc that is opened or closed to control the draft (the air reaching the fire so that it burns more or less strongly) (вьюшка (в печах), регулятор тяги, дымовая заслонка) ==> a person or thing that damps or depresses (то, что или тот, кто подавляет, оказывает угнетающее воздействие).