Mostly you would say something is "the shit" if it's bangin or something, but if it happens to be particulary phat, you could elaborate, saying something is "the shit's tits" being the best or most valuable part of the shit, or the "best of the best."
igg 1: You ever had Smirnoff Ras with Cranberry and Grapefruit juice?
igg 2: Yeah dude, that stuff's the shit's tits!
Vince: hey Ralph you see that stripper over there.
Ralph: yea, she definitely has some shits for tits.
Vince: we need to get the fuck out of here.
Ralph: i can almost smell them from here.