What is Keep Your Mouth Down?
A variation on the common saying, "keep your voice down", but with more emphasis on physically keeping the mouth out of sight and harm's way.
Secondary usage of the phrase:
Also used when receiving oral pleasure and the giver lifts his or her head at an inopportune moment, typically before climax or orgasm.
Bob: No, those girls totally reek of cigarette smoke, no way would I think about hittin' that.
John: Damn it Bob, keep your mouth down, they are right behind us.
Jimmy: Damn it, Jessie keep your mouth down, I was about to finish!