Inside jokes are a language with a population of three. Protect them; they’re proof of history.

Inside jokes are a tiny language with almost no speakers, and that is their whole value. A phrase that means nothing to anybody else is proof that you were both there, that the night happened, that there is a shared history long enough to have shorthand. These things fade quietly when nobody uses them, and the fading is how friendships end most of the time, without a falling out.

Send one of yours to the person it belongs to this week. No occasion needed. Keeping the language alive is most of the work of keeping the friendship.