Say you're walking into work, putting your stuff down. All of a sudden, you hear your coworker shriek "RAISIN COOKIES?!" Her yell is followed by a stuffy, higher-up's laughter. You jerk your head toward her cubicle like a deer in the headlights. Food?
The coworker catches your eye and smiles. She laughs with the higher-up again, something about desserts and flour fights. You make your way through the cubicle maze, thinking that this laughter thing is definitely something you can get in on because why would that coworker invite you over with that twinkle in her eye if this was just an inside joke?
You tumble over several boxes and recover by pretending to tie your shoes. You hope that this joke is really good because you have to walk so far. You're formulating some theories as to what the joke might be about. Oatmeal-raisin"trust" issues? A picnic gone wrong?
You finally make it to her cubicle, only to find the topic of discussion has changed. "Raisin cookies? Oh, it's just an inside joke. Did you get that stuff mailed yesterday?"
Oh, the pain. The pain of an inside joke.