bad-mouth (v.)youdaoicibaDictYouDict[bad-mouth 词源字典]
"abuse someone verbally," 1941, probably ultimately from noun phrase bad mouth (1835), in Black English, "a curse, spell," translating an idiom found in African and West Indian languages. Related: Bad-mouthed; bad-mouthing.[bad-mouth etymology, bad-mouth origin, 英语词源]