My blocklist is 30~40 users long. [For reference, my blocklist in Reddit reached 400 or so.]
To keep it short, I typically block people who, egregious or consistently:
show lack of reasoning, even if I agree with the conclusion
misrepresent what others say
take things off context to judge them, even if I agree with the judgement
vomit lots of "hard" certainty on things that they cannot reasonably know (e.g. the others' emotional states over the internet)
engage in passive aggressiveness (note that I tolerate some clear hostility, just not pass-aggro)
show clear signs of sealioning (e.g. "I don't understand" + misrepresentation of what someone else said)
tell others shit like "trust me" = "I expect you to be a gullible piece of rubbish"
Note that "egregious or consistently" are key words here. Like, I'm not going out of my way to block someone out of a brainfart; this is not some sort of petty revenge, it's just removing from my sight people who I believe to not contribute with my overall Lemmy experience. I also don't take issue when people block me, for whatever reason they might have.
I'll reply to myself to avoid editing the above. The other user made me realise that what I said about pass-aggro is unclear - since the expression is used with multiple meanings.
In this specific context, by passive aggressiveness, I mean "an utterance showing politeness as a disguise for rudeness".
I'll give you guys an example. Imagine that Alice says "I saw a potato tree today". And Bob replies to Alice one of the following:
"Potatoes do not grow on trees."
"Potato tree? Are you braindead or what?"
"Yeah sure, and I saw some unicorns today. Because you know, potatoes totally grow on trees, right?"
"Oh dear perhaps you're a bit confused, so let me enlighten you. Potatoes do not grow on trees. I understand that this might be a bit too complex for you to understand, but put on some effort, okay?"
The first three are not pass-aggro. #1 is simply dry (no attempt at politeness or rudeness); #2 is simply rude (I'm typically OK with that within limits). #3 uses irony and sarcasm in such an obvious way that it comes off as simply rude, there's no attempt to use the irony to disguise the insult. Only #4 is pass-aggro, as it calls Alice stupid and lazy in a disguised way.
I tend to block people who do this because they rub me off the wrong way - it shows a lack of dignity to be upfront that you don't see in plain rudeness.