wet blanket
US /wɛt ˈblæŋkɪt/
UK /wɛt ˈblæŋkɪt/

1.
aguafiestas, cenizo
a person who spoils other people's fun by being negative and unenthusiastic
:
•
Don't invite John to the party; he's such a wet blanket.
No invites a John a la fiesta; es un verdadero aguafiestas.
•
She's always being a wet blanket, complaining about everything.
Siempre está siendo una aguafiestas, quejándose de todo.