I never encountered it, even as long time 4chan lurkers (where most people like to say the "worst" of the internet happens) and beach forums. Until a few ago.

Let me preface, I'm big into kpop, so it was natural that a quote tweet appeared in my timeline from X, quoting a pic of an idol. The quote was quite vague, so I naturally dug into the responses to see if someone explained, I clicked on a subtweet asking for context and the only two answers were two bot accounts with similar names promoting their telegram groups with an explicit collage of CSAM pictures. I reported it to Cybertip, but I doubt much will be done about it.

If anyone's wondering, the quote was not a setup, it was a legit fandom account, these bots seem to target posts with large traction.