If his orientation is asexual, then masturbation would prove an ironic act in opposition to his disposition. He could also use the act as a tool of power irony, because it excludes women in a nonaggressive, but entirely bold way. And lastly, it could be color irony – if he is nonwhite, then the violent self-production of literal whiteness can serve as ironic proxy for empowerment; he is reclaiming white for himself in a base and masculine way.