A person who routinely inhales and exhales through the mouth, instead of through the nose. / (idiomatic, slang, derogatory) A person who is boorish, stupid, or otherwise unattractive.

foot-and-mouth disease

(intransitive, slang) To complain or otherwise express oneself in a loud, immoderate manner. / (transitive, intransitive, slang) To talk impudently, especially to one's superior.

simple past tense and past participle of mouth off

Alternative spelling of mouth breather

(idiomatic, used in similes) An indistinct, muffled or garbled manner of speaking.

(informal) Regularly using vulgar language, especially strong profanities.

(idiomatic, euphemistic) The characteristic of regularly using vulgar language, especially strong profanities. / (idiomatic) A person having this characteristic.

Tending to use obscene or offensive language.

(idiomatic) An authentic source; someone who directly experienced or witnessed something.