悪わる口ぐちを言いう

expression, godan verb (-u)

speak ill of; bad-mouth; insult

Used for saying negative things about someone, often behind their back or in a disparaging way. The object is marked with を.

• 彼かれはいつも人ひとの悪わる口ぐちを言いう。

  He always speaks ill of others.

• 陰かげで悪わる口ぐちを言いうのはよくない。

  It's not good to bad-mouth people behind their backs.