When I called to laugh about it, she got unexpectedly poignant—when we're dead, she said, no one will know about this.
No one knows now, that's what makes it special. That only 2 people find something funny (or meaningful) is part of how it connects them. If all those connections were visible, the world would be full of, y'know, fireworks & rainbows & unicorns. And it's still just between the 2 of us even if we tell everyone.
I assume everyone with a family or a deep friendship must have inside jokes like this. Right?