Sourpuss

Noun

 * 1) A person who is habitually gloomy, sullen or miserable

Thesaurus
bellyacher, brooder, complainer, crab, crank, crosspatch, depressive, gloomy Gus, griper, grouch, grouser, kicker, killjoy, malcontent, melancholiac, melancholic, mope, sorehead, spoilsport, wet blanket

Etymology
“sour” (bad-tempered) + “puss” (slang for “mouth”)