The result of a person (or organisation) disappearing so far up their own backside that they warp a hole in spacetime from which not evenlogic can escape.
I came perilously close to the event horizon of a brownhole today and frankly, I'm lucky not to be buried in a whole heap of super-dense shit.
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"
"We Been Dancin' with Mr. Brownstone
He's been knockin he won't leave me alone"