I once had a narcissistic friend who I finally got tired of and one day I just told him he had failed me and then cut ties with him after that. Lol I think that's like the worst thing a narcissist could hear.
Now with that being said, I'm a little quicker to pickup on a narcissist or at least know something is off with them. There's this one girl I was talking to that you couldn't have any type of rational conversation with her because she would assume it was all her fault. I finally got tired of her too from her wasting my time and one day I go what do you even do in your free time for fun? Last I heard of her too. Lol I would always try and arrange fun things for us to do and she would never follow through. It's all about them they only care about their feelings nobody else's.