There should be something against reddit's rules in stalking people's post history on unrelated subjects, and then insulting them on it... on a thread that has nothing to do with it.

Otherwise you get tribalism and wars. You will get BLM people arguing with conservatives, or religious people arguing with atheists all over subreddits.

Its not helpful. Don't bring this stuff up.

I left that exact comment on a thread recently, and its getting downvoted as we speak. After some idiots and liars and haters started stalking me and started making accusations that "my post history is disgusting".

Actually my post-history is clean even, I'm pretty calm and well explained, I don't even make personal attacks. I just stick to the topics. But I think, that if you leave a comment saying "good luck bro" to a man suffering from false-accusations, that is a "disgusting comment".

Anyow, so are there rules about this? About bringing up topics in someone else's history?

Let's say we are on a apple-pie baking sub-reddit. And I say "apple pies are better with a lot of butter", and then someone else says "oh no you are so stupid, I hate you, also you are disgusting MRA, your pies taste so bad because you are a MRA".

Isn't that kinda... against reddit's rules?

If so, which rule specifically? It is a bit like brigading... where you "post a link to someoen else's messages to start arguments". Except now they are "posting a reference to someone else's messages to start arguments".

It is brigading, right?

Http-links vs verbal references to a thing that other people can easily find if they make one-click and then hunt for 10 minutes of quite tame conversation for something they don't like. Thats the only difference.