open (one's) mouth(redirected from opens their 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.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
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?
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