lollygrabber
a person who criticizes, objects to, or opposes something. One that takes the fun out of life. Synonyms: naysayer, cynic, complainer, defeatist, downer, killjoy, misanthrope, sourpuss, party pooper, curmudgeon, crank, kvetch, Debbie downer.
He's quite the lollygrabber, always complaining about the food wherever we go out to eat.