Marble Cake may be used as either a noun or a verb; however, in either context it describes the action of a man anally penetrating either a man or a
woman and ejaculating inside of said
person. Afterwards the
person on the receiving end defecates. If the defecator is a man, he then masturbates into his own feces.
Finally, the resulting mass of feces and ejaculatory fluids is put on a platter and one or both parties partake of the "cake."
This is similar to Felching.