The word "killjoy" refers to a person who ruins the fun or joy of others by being negative or discouraging.
Sentences with «killjoy»
Join Hardlydan, Amras89, Yodathethird, and Saint Killjoy for game talk and fun! (thegamesmen.com)
Such killjoys could include anti-trust or other negative government action, stockholder disapproval, withholding of tax rulings, etc... However, the predictability coupled with a short holding period produces quite decent annual rates of return. (novelinvestor.com)
But she got this really sad look on her face and I realized that I was being a real killjoy. (littleheartsbooks.com)