Thats next level echochamber. Do people actually do this?

Yup, even custom css to help point out who you should downvote.

That's really interesting. Can you point to a github repo or chrome extension or something?

These groups tend to be invite only and don’t publicly post this code as it reveals usernames of people on blacklists, but if you search around discord channels or some subreddits you might find them.