It currently depends on which client you're using. The devs are working on building it into the server side, but at least 'connect for lemmy' on android allows you to block instances yourself.
sh.itjust.works Main Community
Home of the sh.itjust.works instance.
Not that I know of, but it should be added in for those who don't want to interact with people from Hexbear. If people have the freedom to block an instance for themselves it would expand the decentralization that Lemmy is built on, since people don't have to move to those instances to block out Hexbear.
I've read that blocking the Hexbear domain is a solution to this, but that isn't a proper solution, since those who aren't tech-literate would have a pretty hard time doing that, so a first-party solution would be the best.
any time i see a weird gif reaction i just block.
it gets repetitive, but that's the way it is for now.
at some point i might just move away from shitjustworks to an instance that actually cares.
If you are on browser using unlock origin, you can use custom cosmetic filters like sh.itjust.works##div.post-listing:has-text(/hexbear.net/)
. Not perfect and does not hide comments, but I've been happy enough with just this.