Because I love xkcd so much, I'm going to open with this.
Human beings, when they're talking to people they know pretty well, have inside jokes. They make references to past experiences and conversations. Interesting characters will do this as well.
Don't believe me? Watch this clip from Love Actuallybetween 5:42 and 6:00.
Now, come on, isn't that an absolutely fabulous opening?
In that opener, we get a sense of who each guy is and just how well they know each other. Because they've got these shared experiences they can reference talking to each other.
Inside jokes -- so long as they're explained enough that one knows they're inside jokes -- can be a great way of explaining just how long characters have known each other, how well they know each other, and -- depending on the joke -- can provide hints to back story that might be apparent later.
So, how about those zebras?
Do you like inside jokes? Do your characters tell them? How do you feel about character's rehashing shared experiences and telling inside jokes?