It is a statement regarding poopy. It refers to excrement and the human predication to refer to slang words in the negative of their meaning. Shit is good, and to be shit in the slang world is a good thing and to be 'shiznit' or 'the shiznit' would elevate you in the heirarchy of your 'homies' or 'nizzles'. Often used in rap videos, or by causcasian youths trying to fabricate the experience of being an african american. Also, in slang -'Honky wiggers perpetrating like a mug' In this case, acting in this way would not be the 'shiznit'
See also - Malibu's Most Wanted; Snoop Dogg; Any white guy in Philly, NYC, and Little Rock as see on HBO.
My friend, you have done something that resembles the qualities of fecal matter. Excrement my fellow man, you are waste byproduct from human waste. Or..You mofucka, dats da shiznit. Shiznit bro you da shiznit. Word.