You can remove or change any insults which don't fit in the context, to make sure your stream of nastiness is just right, even when it's just wrong. If there’s some text you want to nastify again and again, you can add a Siri shortcut to create a new nastified version of it in response to a voice command. In the Shortcuts app, you can also use the 'Nastify' shortcut to add insults to the result of another Siri command, or ask for a random insult.