A term used to tell someone to get down because bullets are going to be fired in their general direction in the immediate future. The general idea behind wording the phrase this way is to let your friend know what is about to happen whilest leaving your helpless, soon to be, victims in the dark.

Used by Bullet-Toothed Tony in the movie "Snatch"

When you eat dirt for the first time and leave your family to build a shack in the woods