The Jargon File (version 4.4.7, 29 Dec 2003):

RTFB
 /R?T?F?B/, imp.

    [Unix] Abbreviation for ?Read The Fucking Binary?. Used when neither
    documentation nor source for the problem at hand exists, and the only thing
    to do is use some debugger or monitor and directly analyze the assembler or
    even the machine code. ?No source for the buggy port driver? Aaargh! I hate
    proprietary operating systems. Time to RTFB.?

    Of the various RTF? forms, ?RTFB? is the least pejorative against anyone
    asking a question for which RTFB is the answer; the anger here is directed
    at the absence of both source and adequate documentation.


The Free On-line Dictionary of Computing (30 December 2018):

RTFB

    (By analogy with RTFM) Read The Fucking
   Binary.

   Used when neither documentation nor source for the problem
   at hand exists, and the only thing to do is use some
   debugger or monitor and directly analyse the assembler
   or even the machine code.

   "RTFB" is the least pejorative of the RTF? forms, the anger is
   directed at the absence of both source *and* adequate
   documentation rather than at the person asking a question.

   [Jargon File]

   (1995-08-20)