Run (one's) mouth phrase
If you "run your mouth", you talk non-stop and nonsense, especially in an annoying way.
He kept running his mouth until his mom got really angry.
Katherine admitted that her tendency to run her mouth could get her into trouble
The young lady has run her mouth since the early morning.
The verb "run" should be conjugated according to its tense.
Used to refer to a person who is your enemy
He faced his sworn enemy.