When you're so down bad that you need an extension of the phrase to define just exactly how down bad you are. This version of down bad doesn't always have to be applied sexually. It could mean you're down bad for a delightful date, or you're just doing shitty in life overall.
In other words, you're either doomed or desperate as hell.
Chad: "Bro, my girlfriend broke up with me AND I failedfinals."
Brad: "Man. You down badarious, dude."
12 step recovery jargon referring to someone new who talks about how great life is, now that they'resober. Usually meaning that the person is out of touch with reality.
The new guy seems pretty happy for a dude who has no job, no money and no family. He must be on a pink cloud.