Abbreviation of Denied, or De-Ne-Nied, which came from the beat of the theme music in the movie S.W.A.T. .It is commonly used to insult someone, telling them they got denied, or when an eventturns out bad/sour.
-you nearly got DNN!
-hahah, man he DNN you bad!
-That trip we organised last week got DNN!
-My date got DNN man.