throw a wet blanket on

The phrase "throw a wet blanket on" means to dampen or diminish excitement, enthusiasm, or joy about a certain thing or situation. It implies that someone's pessimistic or negative attitude is spoiling the positive ambiance or atmosphere. It can also refer to discouraging or putting a damper on plans, ideas, or festivities. Just as a wet blanket dampens and reduces the warmth and comfort provided by a blanket, this phrase implies that someone is extinguishing the positive emotions or good vibes associated with a particular thing or event.