Talking too much! Running your mouth!
They didn't know any of it, but you kept runnin' that yap!
mouthing off, talking shit or just being loud.
Quick for running your yapper
Dicky - "What was that guy sayin about Celtics tickets back there"
Biff - "You mean that dude runnin yap at Billys? I don't know, alls I heard was blahblahblah n rarara"