A noise that comes from the air of a queef or a fart travelling over the veins of a man's erect penis during sexual intercourse. Every man has a different dickwhistle because every man has veins in different places and of different sizes.
Billy's dick whistle is short and high-pitched because he has a small and not very veiny penis.
Jamal's dick whistle is long and triumphant, like a trombone.
"Dick In Mouth" or "D.I.M" is an acronym for someone(usually a guy) whos is basically an idiot, acts like a retard or is simply a dumb fuck and would look better with the "dick in the their mouth"
"Hey dick in mouth , what the fuck are you doing over there? You gonna get that done or pound salt up your ass?!"