"Oh. Personal," is what he says to that. He gets the idea of things you keep to yourself in theory, he does. But it tends to fall apart in practice where he's concerned and he can't come up with an effective response. Also: personal? Give him a moment - it needs to sink in before he catches up with that particular statement and devotes more of his attention to it. In the meanwhile: "What's wrong with telling him himself?"

And then it dawns on him.

"Wait, personal?"