OK, back to my post...
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I have this little joke that I make, about an egg salad sandwich. I think it is the height of hilarity, but then I remember that no one really has any idea what I'm talking about or why I'm cracking up. The problem is, it's an inside joke-- one that came about from a real circumstance, got blown up into a joke among friends, and then I forget that not everyone was there. And without the backstory, it just isn't as funny.
(Keep in mind that this may actually be funnier if you were there...)
One day, many years ago, hubby Matt was telling someone about the egg salad sandwich he ate for lunch. It wasn't exciting, it wasn't anything special, and he was as bored talking about it as the other person was listening to him prattle on about egg salad sandwiches. So he stopped. In the middle of the sentence, he just stopped and wondered out loud why the @#)! he was talking about egg salad sandwiches. The other person agreed.
So these days, whenever someone is talking our ears off about THE most boring subject ever, we just say, "I had an egg salad sandwich..." (and sometimes we mention the creamy mayonnaise, or the fluffy bread, or another boring detail)
Hilarious to us, but probably confusing to others.
I do have to congratulate Valerie Geary for getting the joke when I used it to describe my feelings toward most Twitter posts, but for the most part, it confuses people.
Which brings me to my writing-related point: making sure there is nothing in my WIP that is an inside joke.
When you cut and paste and rework and rewrite as much as we all do, a lot of wordy backstory gets edited out. BUT BEWARE! If you cut all that backstory, you may do it at the expense of clarity. This is probably the best reason to use Betas (or at least have other eyes reading your WIP), because they can spot things you can't-- namely, when you've removed a chunk of backstory which has left your character doing something that doesn't make sense. You don't notice it yourself because it is like the egg salad sandwich. You have all the context and backstory in your head, but remember, your reader wasn't there. So drop the inside jokes! Or for crying out loud, at least explain them!