A rhetorical question used when one is in a difficult predicament and the circumstances suddenly change in his/her favor, such as when the person in trouble pulls out a gat or when his/her posse shows up ready to whoop some ass. Often followed by "bitch" or "punk" to further assert dominance.
Barack Obama: "Now that I've won the Iowa caucus, I have the Democratic nomination in the bag. The New Hampshire primary is going to be a walk in the park."
(Hillary Clinton wins New Hampshire primary)
Hillary Clinton: "Hell yeah! What's up now, bitch???"
(Barack Obama wins the Democratic nomination)
Hillary Clinton (obviously insincerely): "Congratulations, Senator Obama. I am so happy for you. The American people definitely made the right choice."
Barack Obama: "Three words, Senator Clinton: WHAT'S UP NOW?!?!?!"
Now listen up you fat fuck is what you say when you are going to start the most fire rant of 2016.
When that dude calls you irrelevant.
"Now listen up you fat fuck..
I'M EX PLUG DJ, I WAS ONE OF THE FIRST DUBTRACK MEMBERS. I MADE THE SKYPE COMMUNITY. I AM SKYPE I'M THE NEW GENERATION OF KARMAWHORING. AND I'M IRRELEVANT? PISS OFF WITH YOUR SHITTY BALL'ON TALK CRINGE BULLSHIT. THE ONLY REASON ANYONE WOULD EVER VOTE FOR YOU IS THAT THEY SAW YOUR MISERABLE FACE AND FELT LIKR THEY HAD TO DO IT OUT OF SYMPATHY. NOW SHUT THE FUCK UP AND GO BACK TO THE CAVE YOU BELONG IN."