Reference to the female vagina. A depository for a dude’s blast of nut custard.
Alternatively, reference to a condom or sheath used during sex to prevent nut custard from entering the vagina during a vigorous pounding of the cervix.
Rachel has a stank ass custard sleeve. But I dropped my load in it anyway.
I banged that toothless homeless lady in the alley. She was dirty but I wore a custard sleeve so it was all good.