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 fucking Jessica
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, stoprunning your mouth, your only going to piss them off even more!'
A "human" that spends so much time playing video games that their posture is level nerd neck. Everytime anyone goes tryhard they hunch down and their neck gets longer there fore a nerd neck is always hunched down cause they're always going try hard. In other words a nerd neck is a try hard, since their neck is 100% longer than the average human being due to playing too many video games and taking them serious, nerd necks are not even considered human anymore but something more sad. Nerd necks are often found on fortnite, their natural habitat usually being tilted towers.