Opened mouth - Idioms by The Free Dictionary
open (one's) mouth (redirected from opened mouth)
open (one's) mouth
To say something, especially that which is indiscreet, boorish, or meant to be a secret. Why did you have to open your mouth about my crush on Tommy? Why couldn't you just keep it between us? You've got to make sure that he never opens his mouth about what went on here today.
open your (big) ˈmouth (informal) say something when you should not: Why do you always have to open your big mouth? Can’t you just keep quiet sometimes?
References in periodicals archive
We were faced with so many opened mouths
and dazed expressions that we asked our buddies over at YouGov Siraj to see if the few we met were the exception.