One of the greatest things in the world is an Inside Joke.
The fact that you can have an entire conversation or sequence of events summed up in a phrase or a glance. Shared history always helps, but it doesn't always have to be part of it.
Say two words.
Raise an eyebrow at the right time.
Quote a movie.
If anyone within a five foot range either laughs or says anything relevant, they are in on it.
And it's fucking great.