Noun
One who rails; one who scoffs, insults, censures, or reproaches with opprobrious language.
Source: Webster's dictionaryWhen one told Plistarchus that a notorious railer spoke well of him, "I 'll lay my life," said he, "somebody hath told him I am dead, for he can speak well of no man living." Plutarch
A customary railer is the devil's bagpipe, which the world danceth after. Danish Proverb