I send my friends little cards with a picture of me hanging out with my new friends. In word-art superimposed on the picture it reads "You weren't cool enough". From that moment on, I make the very conscious to never refer to them as a friend in conversation again but instead say acquaintance. I then make sure to also not contact them anymore, and not see if they've contacted me. And if they have, I ignore those text messages, or send a fake message back reading "this number isn't in use anymore. or this phone recognized your number isn't cool enough."
Because I think friendship is all about social mobility. You just climb the shoulders of 'the lessers', as I like to call them. Because friendships end purely by me deciding to no longer put in effort. If they still do, fuck them, I'm moving up in the world. Soon I will be king and they shall bow before my golden sandals.
I think it's very important, personally, to know when a friendship is ended. Because putting a label on it exonerates me. I'm not messaging them, they haven't messaged them for a year, they don't deserve it anymore. And, yeah, sure, I didn't message them either. I have a clock. 219 days, after that done. Don't try to reconnect, hun.