Not gonna lie, I thought this was a play on the character "Darth Bandon" from the Star Wars Extended Universe. It is not - in fact, it is a political meme.
That being said, like most of these things, it is completely nebulous and has no substance in and of itself - it is inherently valueless and says nothing about the user of the phrase. That is to say, a person using "Dark Brandon" for its intended use is a coward.
Person A: You may have defeated the pathetic bounty hunter my Master sent after you, but you are no match for me! I have studied at the foot of the Dark Lord himself!
Person B: LET'S GO DARK BRANDON
Person A: Your words mean nothing to me... unless you wish to beg for your life. No? Then I shall try to make this both quick and painful!
A Dana is a beautiful individual and is the best person you will ever meet. Dana is smart, athletic, and the hottest person in the school. Dana is an amazing kisser, and is great at everything!