A diabolical, evil and cunning person, that you hate because he ruins peoples lives and has no morals. They are the world biggest crooks and are real hypocrites.
Example:"Don't trust that the guy, he's a Black Snake!"
When the DEA raids dispensaries of weed (typically in California, where weed is semi-legal), the agents - who are dressed head to toe in black - stand in a line and hand things down the line very fireman-water-bucket-line style. It looks a lot like a black snake slithering.
I was going to get some weed today, but the Black Snake came through so I'm still dry.