Railer

(n.) One who rails; one who scoffs, insults, censures, or reproaches with opprobrious language.

Thesaurus Entries

Cassandra, Eeyore, Thersites, backbiter, belittler, calamity howler, calumniator, caustic critic, debunker, decrier, defamer, defeatist, deflater, depreciator, derogator, detractor, disparager, hatchet man, killjoy, knocker, libeler, malist, man-hater, misanthrope, misanthropist, misogynist, muckraker, mudslinger, negativist, nihilist, pessimist, prophet of doom, railer, retreatist, seek-sorrow, sexist, slanderer, social critic, traducer, woman-hater, worrywart