A fork of Rural Dictionary
Shortened for deus ex machina, a term used to describe sudden plot twists in works of anime, movies, and other stories, normally involving a hero's fight against a villain, and favoring the hero, allowing him to win by otherwise unused methods within that fight.
DEM normally involves the hero getting beaten to a pulp until somehow ascends in power and uses that to destroy the villain in a matter of one or two hits.
Essentially the same thing as, "Damn it," or, "Dammit," but can be said without consequence because it isn't actually swearing.
Brittany:I beat you're grade by 1%.
Morgyn: Dem it.
Some black dude that hangs around with girls, he's also a bit of a poof.