watch (one's) tongue(redirected from watch their tongues)
watch (one's) tongue
To be very mindful or cautious about what one says; to keep a check on one's language or control what one says. You'd better watch your tongue around these parts, mister, or you'll find yourself on the wrong end of someone's fist! After being threatened with failure for my snide remarks in class, I knew had to watch my tongue for the rest of the semester.