the word itself is probably a 4chan thing, if I were to bet anything. but it's normalization may have been a weird twitter thing
@SuricrasiaOnline I've heard rumors that the word "shitposting" came from SA, but they used it to mean "making really bad posts in a thread to derail or tank it"
@BestGirlGrace @SuricrasiaOnline we weren't active on sa back in the day but from our limited reading of let's plays and occasionally reading other public threads this sounds familiar
seeing tweets that use "shitpost" as we use it today as far back as 2009