gettin' funky on the mic' like a old batch o' collard greens

rapping in an interesting, different and unusual (yet likeable) style is considered "funky" rapping, and this is compared to how funky (very bad smelling) a batch of collard greens can get if they sit out at room temperature for a while after being cooked
bill
Implying that he is as funky when he raps, in a good way, as the funky smell of an aged pot of boiled green onions, garlic and bacon fat.
gurper707