"Deer in the headlights" is a good description. Particularly when she gets to the "Why don't you just fix it?" part, often the only response that comes to mind at the time is "Why don't you just get a sex drive?" Knowing just how unhelpful that would be, I keep my mouth shut.
I tried stopping the conversation and scheduling an appointment several months ago. It worked -- until it was time for the appointment. Then, she quickly became all upset because I tried to pick up where we left off, and she expected that I would have worked up solutions in the intervening 24 hours (that I haven't been able to come up with in nearly 20 years of marriage).
I do have a copy of Crucial Conversations; hopefully I can get it read over Christmas break. Thanks for your suggestions; I'm still open for any others, as well as any (particularly female) insights into the whole episode.
HERE is Edward Bear, coming downstairs now, bump, bump, bump, on the back of his head, behind Christopher Robin...sometimes he feels that there really is another way [of coming downstairs], if only he could stop bumping for a moment and think of it.