Thanks. I had a hunch. I'm familiar with "RTFM", but would probably get equally confused if "TFM" was used as a noun.
I suspect the chronology is something like RTFM -> TFM -> RTFA -> TFA, but the second and third might be switched. Dropping the R does introduce obscurity, but being able to convey the underlying sentiment (that while the content could/should have been consulted, it seems as though it was not) without a verb allows for a nonconfrontational syntax similar to passive voice, but even moreso, and often without obvious "weasel" effect, to boot!
Makes a lot of sense, thanks! Maybe it's also useful since the R is read explicitly as "read". Hence "they should instead be RTFM" sounds grammatically wrong. Breaking off the verb allows for a more natural read. It's funny how an abbreviation can carry more information than whatever it's short for.
And I believe this slang came from Slashdot, which is like the Hacker News forum in the decade before Hacker News
Interesting, I didn't know it came from Slashdot! I spent quite a bit of time reading it in the early 2000s, and sometimes miss the subculture and not always subtle jokes (beowulf clusters... ). The moderation system encouraged jokes (there was a specific 'funny' tag), unlike HN which does not 'orient' things, and happens to be very serious.