She knows where the pants are
Really, this is all about the clever quips it inspires:
A friend of mine has just experienced the defining moment of any new live-in relationship - the one where your man asks where his pants are. This wasn't a bad man, a sexist creep, a cad. As a rule, he could be found seeking her opinion on the new Philip Roth, the Scissor Sisters, or the merits of a restaurant they had just visited. Now, suddenly, surreally, he was asking her about his pants. Where were they? What had she done with them? Could he have a fresh pair, please?