expression, i-adjective
sharp-tongued; sarcastic; foulmouthed
Describes a person who habitually speaks in a cutting, sarcastic, or harsh way. Often used as a prenominal modifier (口の悪い人).
See also: 口が悪い
彼は口の悪いことで有名だ。
He is famous for having a sharp tongue.
口の悪い友
I'm always teased by my sharp-tongued friend.
口が悪い is a clause meaning 'to have a sharp tongue', while 口の悪い is an adnominal form used to modify nouns directly.
Phrase composed of 口 (mouth) + の (possessive particle) + 悪い (bad). Literally 'bad of mouth', it describes a person whose speech is harsh or cutting.