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1.
More than a simple "fuck you," the phrase "fuck on you" holds more weight, as it implies the quite unmerciful act of dumping 'fuck' on someone. To say "fuck on you" to someone is to imply that this person is so far beneath you, that for you, or anyone else to fuck them, or personally inflict physical pain on them in any way would be stooping to a low that no one should attempt - for this person is not worth the trouble. Rather, "fuck on you" suggests that the essence of 'fuck' - sweaty, terrible penetration - should instead be thrown in the face of this person, perhaps from afar.

Usually used in a boastful manner, the phrase works especially well if the user is being a sore winner of some sort - adding insult to injury.
Nick was beating J so hard at NCAA Football 10, after every play Nick just kept standing up and saying "Fuck on you." He was kind of out of control, and no one stopped him. It was devastating.
by jerusalemcampground April 14, 2010