“I went through your post history and so now I feel confident stereotyping you” is a borderline temp ban red flag, imo. It definitely indicates that the person is tilted hard enough, for one reason or another, to not take the discussion rationally and maybe need a break. If your community excludes certain harmful opinions then a post history check can be helpful for moderation, but using it to ad hominem someone in a discussion forum where all the important information should be in the discussion is flame war tactics and can lead to stalking.

Usually doesn’t happen here to the degree it happens on reddit, but literally this week I had someone do it to try and claim that I hate cars because I post in /c/fuckcars@lemmy.world, even though I own two cars. Indeed, it was a stupid topic that dependably gets some people irrationally incensed, which primed this guy to try and make it personal.