Why does kesey include a description of mcmurphy's first sexual experience?

Because it is irrelevant and beside the point. If you were a Freudian it would

seem like everything in his way of thinking and the actions of his life were a

derivation of that one thing which is by the way heresay and not admissable

in a court of common sense. That was a literary or dramatic point of Kesey,

to demonstrate by example what a bunch of idiots the mental health people

are and always have been, as compared to the idiOSycratic but actual sanity

of the supposedly crazy people. If that makes sense to you, I recommend a

book called Madness and Society, by Foucalt.