"The Shoddy Lands", a short story by C. S. Lewis, first published in The Magazine of Fantasy and Science Fiction, February 1956, available at the Internet Archive; the text is also available at Professor Frederick J. Vetter's web page. The narrator, a young man, by some unexplained miracle gets trapped in the mind of a young woman named Peggy, and sees the world as Peggy does.
Excerpt from a review by Seth T. Hahne:
In the course of his story, Lewis deposits his narrator (and probably avatar) within a world representing the things a particular young woman cares about. Trees and grass are spongy and ill-defined because she doesn’t care about them or their natural splendor. People as well are indistinct smudges, save for men of a particular type whose faces are radiant and women who remain blurs of perception save for their clothing and accoutrements, which are crisp. Likewise jewelry and fashionable gowns are beautifully wrought in this world of hers. Centrally, the narrator finds an enormous, perfected version of the woman, lounging in swimwear (and then nude), a monument to her bloated, self-serving ego. The narrator then, having returned to the real world, is both struck by how terrible and shallow the world of her affections is and how fearful he would be of some stranger being able to witness his own trifling affections through such an unguarded mechanism.
Excerpts from "The Shoddy Lands":
Here I had a new surprise. It was a jeweller's, and after the vagueness and general rottenness of most things in that queer place, the sight fairly took my breath away. Everything in that window was perfect; every facet on every diamond distinct, every brooch and tiara finished down to the last perfection of intricate detail. It was good stuff too, as even I could see; there must have
been hundreds of thousands of pounds' worth of it. "Thank Heaven!" I gasped. "But will it keep on?" Hastily I looked at the next shop. It was keeping on. This
window contained women's frocks. I'm no judge, so I can't say how good they were. The great thing was that they were real, clear, palpable. The shop beyond this one sold women's shoes. And it was still keeping on. They were real shoes; the
toe-pinching and very high-heeled sort which, to my mind, ruins even the prettiest foot, but at any rate real.
[. . . .]
The gigantic Peggy now removed her beach equipment and stood up naked in front of a full-length mirror. Apparently she enjoyed what she saw there; I can hardly express how much I didn't. Partly the size (it's only fair to remember that) but, still more, something that came as a terrible shock to me, though I suppose modern lovers and husbands must be hardened to it. Her body was (of course) brown, like the bodies in the sun-bathing advertisements. But round her hips, and again round her breasts, where the coverings had been, there were two bands of dead white which looked, by contrast, like leprosy. It made me for the moment almost physically sick. What staggered me was that she could stand and admire it. Had she no idea how it would affect ordinary male eyes? A very disagreeable conviction grew in me that this was a subject of no interest to her; that all her clothes and bath salts and two-piece swim-suits, and indeed the voluptuousness of her every look and gesture, had not, and never had had, the meaning which every man would read, and was intended to read, into them. They were a huge overture to an opera in which she had no interest at all; a coronation procession with no Queen at the centre of it; gestures, gestures about