From The Free On-line Dictionary of Computing (19 January 2023):
Prisoner of Bill
PoB
<humour> (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)