Add the worst content imaginable to the page, but don't make it visible by default. If the site strips JS, then use CSS to only show the terrible content when i

Add the worst content imaginable to the page, but don't make it visible by default. If the site strips JS, then use CSS to only show the terrible content when it's shown on that domain. You can use css to check the current domain based on e.g. links. Extra points if you can cause legal trouble for whoever runs the site. If you're hosting rather large files, then you can also hide content by default that will never be loaded on your site, but will load on the other site. Add a large file to your site, then reference that file a few thousand times with query params to ensure cache busting, and then make the browser load it all using CSS when it detects that it runs on the other site.