Kable Roc, Romulis Caesar, and KnowMad are Nefarious XO. Definitions - Nefarious: extremely wicked or villainous. XO - short hand abbreviation sometimes used to signify love. Creating music since 1996, Nefarious XO has been evolving with the times into its present form. A dynamic group operating out of the Pacific North West, known for the ill production and d**e lyrics coming out their lab. Independent hip hop at its best. Feel free to listen and download these selected tracks.