The "people" being discussed are demonstrably, and in most cases, self-identified, as mentally unstable... They are immune to shame, mockery, ridicule, and irony, and often times these stances actually empower them. So then, what is their kryptonite? Being dismissed outright. "Ok, Groomer" as example, is very a effective method of dismissal. There are many other ways, but I suggest to keep it simple.