An extension of the term "fanboy," meant to be used specifically as the derogatory form instead of the basic term.
Some people wear the term "fanboy" proudly and they rightly deserve to as long as they are respectful of criticism and opposing viewpoints along with being polite in the discussion or advocating of the fan-subject. However, once the person crosses the territory from simply being a strong fan and advocate to becoming unreasonable, overzealous, or rude to those that oppose or differ in opinion, they cross from a "Fanboy" to a "Fanbastard."
Such behavior can range from obnoxiously trying to push the subject onto others, praising the subject without accepting the faults, flat out denying any negative criticism of the subject, and any other rude behavior associated in discussing the subject.
That dude is such an Apple Fanbastard!