@Popehat Personally I think the germans have it right "As we say in Germany, if there’s a Nazi at the table and 10 other people sitting there talking to him, you got a table with 11 Nazis."
As it applies to mastodon nazi shows up from some instance? DM the admin on that instance. If he doesn't take care of the problem defederate it, or rather block it and tell your admin to defederate it.