Nasty Mama desires plump, sensitive cunt lips, and you're about to help her destroy her thick, meaty butterfly wings in exchange for a steamy, wet cunt load.
The speaker is referring to their mother's soft, but dirty cotton underwear, warning of a potential leak of poop and the unpleasant scent of MAMA's muffin.
The speaker is aroused by Johnny Walker's portrayal of a white mistress, referring to him as BBC, and describes various sexual actions in the film, including anal creampies and blowjobs.