It isn't a specific rule (as it's usually covered by "don't be rude" or similar), but I have little to no patience towards witch hunters: users who screech and try to denounce other users, based on little to no rational evidence. Bonus points if the witch hunter has poor reading skills, and extra bonus points if claiming "good intentions" in the modmail (my go-to reply is "go pave Hell with them".)

It infuriates me the most because I got a lot of neurodivergent people in my social circles. And I know that this sort of behaviour makes the space less safe for them, since the ND folks will say things that will be poorly understood by the irrationals, and the irrationals will start screeching at them.

Thankfully I didn't get this behaviour in any of my Lemmy comms... yet.