keep a civil tongue

keep a civil tongue (in one's head)

Fig. to speak decently and politely. Please, John. Don't talk like that. Keep a civil tongue in your head. John seems unable to keep a civil tongue.
See also: civil, keep, tongue
References in periodicals archive ?
All he had to do was keep a civil tongue in his head, and his hands off the student bodies and he'd get to maintain his status as the biggest, baddest Alpha male at Indiana University.