Post by Enrico COverlook it, it's not important; you're quite mistaken. This colloquial
imperative is used in a variety of ways. For example, in Thanks so much for
helping - Forget it, it was nothing, it is a substitute for "don't mention
it" or you're welcome; in Stop counting the change - forget it! it means
"stop doing something unimportant" in You think assembling this swingset
was easy - forget it! it means "it was not at all easy"; and in Forget it -
you'll never understand this theorem it means that the possibility of your
understanding it is hopeless. [c. 1900]
Forget about it is like if you agree with someone, you know, like Raquel
Welch is one great piece of ass, forget about it. But then, if you
disagree, like A Lincoln is better than a Cadillac? Forget about it! you
know? But then, it's also like if something's the greatest thing in the
world, like mingia those peppers, forget about it. But it's also like
saying Go to hell! too. Like, you know, like "Hey Paulie, you got a one
inch pecker?" and Paulie says "Forget about it!" Sometimes it just means
forget about it.
http://www.imdb.com/title/tt0119008/quotes