Source : Free On-Line Dictionary of Computing

Prisoner of Bill
     
         (PoB) A derisory term, in use generally among {Unix}
        users, for anyone who uses {Microsoft} products either because
        they don't know there is anything better (i.e. Unix) or
        because they would be incapable of working anything more
        complex (i.e. Unix).
     
        The interesting and widespread presumption among users of the
        term is that (at least at the time of writing, 1998) using
        anything other than Unix or a Microsoft OS (whether {VMS},
        {Macintosh}, {Amiga}) is so eccentric a choice as to be at
        least somewhat praiseworthy.
     
        (1998-09-07)