Why are there so many videos on tiktok of "how to shut a narcissist down"?

None of the lines given would work. The lines assume the person with NPD has a sense of social fairness or shame. They're not playing but the same rules everyone else is. Best way to shut down a narcissist is to treat them like a random begging you for 20p at the bus stop. Just treat them like a complete stranger. Answer in single sentences. Friendly, but closed off. Narcissists thrive on social leverage. Strip them of leverage, they move onto somebody who has it.