It's a frequently requested feature, there's a GitHub issue for it in the Lemmy project, Mastodon does it so it's possible, but it's not available yet.

To my knowledge, the only paths are:

• Whack a mole with new titty communities, as you have been doing.
• Use Connect, which achieves this via client-side filtering. That is to say, it must still download the titty posts, but doesn't display them to you.
• Be a programmer and submit a PR to improve Lemmy, lemmy-web-ui, or the app of your choice to add this feature somehow.