What does McMurphy accomplish by asking the Nurse about the "inch-by-inch measurements" of her breasts? How does this emphasize his power?

One of the things that Nurse Ratched lives by is a certain power that almost makes her seem manly. She hides behind a facade of powerful, manly arrogance and does not use her femininity in any way. She does not want the patients to think of her in that fashion. By approaching her about the sized of her breasts, McMurphy is bringing up a subject she does not want to deal with; if only for a moment, he is in charge of her and asserts power over her thinking that he has not had earlier.