1
general::
A person who discourages enjoyment or enthusiasm, as in Don't be such a wet blanket? the carnival will be fun! This ex pression alludes to smothering a fire with a wet blanket. [Early 1800s]
American Heritage Idioms
2
general::
Phrase(s): a wet blanket
Fig. a dull or depressing person who spoils other people’s enjoyment. • Jack’s fun at parties, but his brother’s a wet blanket. • I was with Anne and she was being a real wet blanket.
McGrawhill's American Idioms And Phrasal Verbs