To open one's mouth and have incoherent garmble escape will little or no understandable meaning.
Can be likened to when a person combines two words on accident becuase they are thinking one and trying to say the other.
In response to a sentence that makes no sense : "You just shit your face man. Clean that up and talk to me when you're not a retard."
If someone frequently shits their face, they can be called a face shitter