When one "lays out the set," that means they are detailing exactly how and why someone is a total bitch. Laying out the set is often done on the other side of a tinted window where the recipient of harsh criticism cannot see or hear the derision.
As a bus pulls up to an airport, two young, idiotic wangsters might see an airport security officer.
Wangster A: Fuckin pigs, muffucka, I fuckin hate pigs. Fuck you, pig! Fuck you! I'll fuckin kick ya face to the curb ya fuckin pig! Fuck you, pig! Fuck you, pig!
Wangster B: Lay out the set, homie! Lay out the set homey! Yeah, lay out the set, homie!