look up any word, like blumpkin:
 
1.
When someone is said to be “flapping their gums” it means that he or she talks a lot about topics he or she doesn't really understand or know about. It also means to say something but not really mean it.
Frank and Joe are always flapping their gums about what it's like to be street hustlers, when they have never even been out of the burbs.
by girl sexy February 07, 2009