Means Heroin and is also a famous song by Guns N Roses on their debut album "Appetite for Destruction". When they are saying "Dancing with Mr. Brownstone" it means they are "Shootin Heroin"
Synonym for badass, beat, raw, dope. Someone or something that inspires awe. Being brownnasty is the peak of one's life. Few accomplish it, but the ones that do elicit fervent admiration and become members of the brownnasty crew.
Patel: Hey bro, I heard you're the backup qb at Alabama. You must be getting all the chicks, right?
Chandelle: Hell yeah man. More threesomes then I can even count. It's safe to say I'm brownnasty.