I’ve had 2-3 experiences like that on Lemmy and kbin, but far more on reddit. On Lemmy it tends to be “intelligent but deranged person who hates you” while reddit tends to be “insane or unintelligent person who hates you”.
I debated it for quite a while because they were legitimately trying to have conversations, but they were tankies and rather aggressive. Finally just pulled the trigger and I’m happy I did.