In the Castle season 1 finale, "A Death in the Family" Kate Beckett is devastated when Castle does the one thing she asked him not to do, look into her mother's murder.
Beckett: (Clears throat) Ahem. What's the deal with men and boobs, anyway? Castle: Biological. We can't help it. Beckett: But doesn't it bother you that they're so obviously not real? Castle: (Pauses) Santa's not real. We still love opening his presents.