I do some blocking with my hosts file, and I used to put 127.0.0.1. That hits my default nginx vhost, so i usually get 404 or 403 pages which is not so bad since my default vhost is an empty docroot. But it is not very intuitive and sometimes I think a server is down because of the nginx error page before I realize its my hosts file. I considered making a custom error message for my default host to remind me what I'm hitting, but I'm lazy.