These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Alternative Character Interpretation: Ratched is just a nurse trying to do her job as well as she knows how; McMurphy, a racist and statutory rapist, insists on causing mayhem on her ward.
McMurphy himself, who is diagnosed in the play with a pathological need to flout authority and be the center of attention... Which seems about right.
Harding may not be gay but just a feminine man who was constantly berated and put down most of his life for his effeminate nature. In adulthood his self-esteem was nonexistent and he married an attractive but horribly abusive woman to feel and be perceived as more masculine, ironically making him less secure and more submissive. With Homosexuality being thought as a mental illness, sexuality being labeled as black or white and Masculinity be the status quo in the 1960 and the term Metrosexual not in American lexicon till mid 1990 it is very possible. One possible interpretation of it is that it's a symbol of how we have been so socially condition to act and behave in certain manners that we will go through abuse, life risking situations and even death to fit in others people designated roles for us.
Ambiguous Disorder: Of all the supporting cast that get focus, no one has an explicitly given mental illness that puts them there, putting it all up to speculation. Chief seems to have some form of schizophrenia with his visions of the mists.
Hilarious in Hindsight: Big Nurse Ratched's name has taken on a funny quality now that "ratchet" has become teen slang used to describe anything with the quality of the ghetto about it.
Ho Yay: Plenty in the novel, but not between any specific characters and used more to build up the discomforting, emasculating atmosphere of the hospital than to establish the sweetly ambiguous kinds of relationships that the trope is associated with.
In the film, there's Billy/McMurphy. McMurphy even says to Candy something like, "I just want you to do this one thing for me. He's cute, isn't he?"
And then there are the orderlies. According to Bromden, they love to give patients showers. They always check the patient's temperature at the same time they shower the patient, and they go down to Miss Ratched beforehand to get a rectal thermometer and a bottle of Vaseline. She admonishes them to use the minimum amount of Vaseline necessary, but they take the whole bottle inside with them, and they turn up the water pressure till the noise makes it impossible to hear anything that's going on inside...
Nurse Ratched might just be a mean and misguided nurse trying to do her job, right up until the point where she threatens to tell Billy's mother about his "bad behavior", knowing full well the trauma that would cause him, which leads to his suicide.
In the book, she has been on the wrong end of the moral event horizon for many years, as she is seen to submit her charges to torture for crossing her (the scene with the germophobe after the fishing trip, the forced anal administration of medication to a patient merely because he questioned what the pills were for), the electroshock 'therapy', and she has also lobotomized patients as punishment for behavior she dislikes. Nurse Ratched is utterly monstrous in the book.
The African-American orderlies are treated a bit indelicately, and McMurphy even drops an N-Bomb. In the book, the orderlies are overtly rapists.
Many people find the book to be misogynist, what with and the idea that matriarchy is akin to castration, and the implication that no woman could/should dominate a "real man." Prostitution and McMurphy's statutory rape charge are treated pretty casually.
McMurphy's charge of statutory rape—in the time the book was written, it wasn't as serious a crime. McMurphy also alleges she told him she was eighteen, and he wasn't found guilty of it, but he does brag about it. The book and movie asks you to see him as an admirable anti-authority figure.
The Woobie: Every character that's not Nurse Ratched or McMurphy at least until the end. Charlie Cheswick and Billy Bibbit come to mind especially, however.