saying smart ass things and generally bitching at a fast pace. Yelling out paragraphs of bitchyness really quickly. Blabbing nonsensical things in an argument just to take up time and have your voice heard.
(the running part means that is is done at a fast pace or else it would be called "walking your mouth")
"they were in a rational argument and she said something that offended him, so he started running his mouth to show his disaproval"
EX.
Him: hey, Jessica Her: My name isn't fuckingJessica Him: fuck, fuck, fuck, man, fuck, just fuck it man, fuck, fuck, fuck
Her: What the hell is wrong with you!?
Him: you need to stop running your mouth.
Her: Uh, I'm pretty sure it's you who is running their mouth.
When you and/or someone else excessively insult or talk bad about someone something, even when directed to stop. usually, the bully keeps this up to the point where the person directed to the verbal assault becomes angry, irritated, or distressed. See talking smack, talking shit talking bad, verbal bullying, back talk
"Dude, stop running your mouth, your only going to piss them off even more!'
It is said of the situation where a person has the bad luck to make contact with his testicles against an undefined surface or object, intentioned or not.
Given the nature of the word, it is more appropriate to design cases where the interaction is made with a moving object, for example, a ball.
Although it is extremely painful for the victim, it tends to be considerably funny to people who witness it.
Today in the baseball game the pitcher took a nutshot; the baseball hit him in the nuts.
Man, I just watched the funniest nutshot video ever.