I have another one, i want to block the entire instance lemmynsfw.com, as it is a porn instance, and i dont want it in my feed, especially at work, and they are popular enough (in relation to all the others) to come up on the main feed.
edit: i don't know how to fix your problem... i just had a hunt through the app...
This isn't a good solution. I too would like to block instances whose sole purpose is to host porn, but I don't want to hide NSFW on other instances: things get marked NSFW for language/triggers, medical gore, any number of reasons that aren't outright porn.