Stemming from the words Sixty-nine and "Om nom nom nom", sixty-nomming is when two people devour each other's genitals with the use of sound effects.
Shana: "Would you mindfingerbanging my pussy next time we sixty-nom? I would sincerely appreciate it."
Jamelle: "No probs babe, perhaps you could glass bottom boat me afterward."
Shana: "Indeed."
Jeff: "I left a bucket of chicken legs RIGHT THEREin the fridge."
Doctor: "And no one else ate it?"
Jeff: "No way! I live alone and the door was bolted!"
Doctor: "...You may have a rare case of 'som "nom-nom" nambulism'."
Commentary generally given from a restaurant table adjacent to a table with one or more fatties regarding their eating habits. Hilarity generally ensues.