What does Boxing Day have to do with boxing?
(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.