Wet blanket

Meaning: a person who spoils all the fun. 

Significado: una persona que siempre estropea la diversión y el buen ambiente.

Traducción literal: manta mojada.

Real examples:

Example 1: “He danced rottenly, he was a wet blanket at a party, he couldn’t play or sing, he couldn’t play polo and his tennis was no better than anybody else’s.  Bridge ? Who cared about bridge ?” (From the book The Painted Veil)

Example 2: “Trump saw that Clinton was a wet blanket on the Democrat’s spirit, and kept on further energizing his own base with increasingly more outrageous statements.” (From The North Star)

Example 3: