It started with someone named Nathan Poe on a Christian forum in 2005. Poe's identity has never been confirmed, but they were apparently an agnostic engaging with some creationists about the origins of, well, everything.
But there were also people in the forum who were not creationists but were instead writing satirical posts about the origins of man and, well, also everything. The problem was that the satire was too good — so good, it became hard to tell which posts were sincerely defending creationism and which were just jokes.
That prompted Poe to write the comment that became forever known as Poe's law:
Without a winking smiley or other blatant display of humor, it is utterly impossible to parody a creationist in such a way that someone won't mistake for the genuine article.
As we've all learned in the years since, this is a problem for most people on the internet, not just those who spar in creationist forums. It's what leads us to wish for a sarcasm font or even a consistent interpretation of emojis and punctuation online.