The fapping post doesn't seem to talk about anything in the thread at all. So I kiiiinda get it. I find stuff like that 3D printed horny 2B statue thread getting locked a couple weeks ago to be more frustrating.
The strictness around hornyposting does make sense since underage lurkers can visit the site, though.
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Having sex in a place kids might be around and see it is definitely not okay. Arguably, having sex in a public place overall is not okay.
If off-topic posting got people banned there would be nobody on this site other than the staff.