It's tough to explain the genesis of inside jokes. But a conversation zigs and zags in an almost stream-of-conscious way, and you end up with something like, "this is exactly what you deserve," which has been a joke between Sarah and I lately.
This is exactly what you deserve. Exactly. The good and the bad.
This breakfast is exactly what you deserve. This relationship is exactly what you deserve.
Sarah: If we ever get married, I think that's what we should have written inside the rings. "Exactly what you deserve."
Later, though, Sarah had doubts about the phrase.
Sarah: It's not entirely nice is it? It's kind of cynical.
Me: I don't know. Maybe it's just a pragmatic way of saying we're perfect for each other.