I remember this movie was quite the buzz in 1976.  Of course, I was too young to see it.  When it came out on video 10 years later, it became one of my favorites.  I watched it over and over again. 

(I'm talking about the film here, not the novel.  They're quite different.)

WARNING: SPOILER

One character is misunderstood.  She's the villain, Nurse Mildred Ratched (Louise Fletcher).  Indeed she is a villain, but her true villainy does not manifest until the climax of the film.  What we right away don't like about Nurse Ratched is actually typical among psychiatric clinicians.  She is authoritarian, manipulative, patronizing, and plays mind games.  They do not brook challenges to their control and if you challenge them, they will make your life hell.  From everything I know about psychiatric nurses and mental hospitals, Ratched appears even-handed compared to those in real institutions, especially in state hospitals in the 1960s, the setting of the film. 

Ratched's treatment of Billy Bibbit (Brad Dourif) demonstrates her lack of ethics and her spite.  After Billy loses his virginity with the prostitute Mac sneaks into the hospital, Ratched's demeanor is not concerned but vengeful. 

Billy: I-I can explain everything....
Nurse Ratched: Please do Billy, explain everything
(Billy glances back at the others and beams from their approval)
Nurse Ratched: Aren't you ashamed?
Billy: No, I'm not. (momentarily losing his stutter)

Nurse Ratched: You know Billy, what worries me is how your mother is going to take this.
Billy: Um, um, well, y-y-y-you d-d-d-don't have to t-t-t-tell her, Miss Ratched.
Nurse Ratched: I don't have to tell her? Your mother and I are old friends. You know that.
Billy: P-p-p-please d-d-don't tell my m-m-m-mother.
Nurse Ratched: Shouldn't you have thought of that before you took that woman into that room?
Billy: I didn't t-t-take her...
Nurse Ratched: You mean she dragged you in there?
Billy:  Y-y-yes...everybody did, Miss Ratched....
Nurse Ratched: Who? You tell me who!
Billy: M-m-m-ma-m-m-m-Mac, mff...mmm...McMurphy.....P-p-p-p-please don't tell my m-m-m-muh-mother!
(Nurse Ratched orders the attendants to set everything in order.)
Billy: (screaming and punching himself): N-N-NO NO NO NO NO!!!!  NO NO NO NO NO!!!!
(Ratched orders the attendents to lock Billy in the nurse's station and watch him unil the doctor arrives, but further disruptions draaw the attendants out of the office.  When alone, Billy commits suicide by lacerating his arteries with broken glass)

Caution: violence, profanity
http://www.youtube.com/watch?v=847k07FB544

Major ethical breach I:  Ratched is a family friend, yet she keeps Billy on her ward.
Major ethical breach II: At Billy's most vulnerable point, Ratched issues a threat she knows will trigger suicidal anxiety in Billy; she says she is going to tell his mother he had sex with a prostitute. 

After discover the bloody suicide scene it would be protocol to call for calm and order, which she does.  The problem is, her sadistical behavior caused Billy's suicide, and R.P. McMurphy (Jack Nicholson) knows it.  Mac lunges and commences strangling her.  The attendants attack Mac, Bromden (Will Sampson) attacks the attendants, and chaos ensues.

Earlier in the film, Nurse Ratched is determined to win the battle of wills over Mac.  She recommends to the staff that they commit Mac to the hospital instead of sending him back to jail, where the psychiatrists thought he belonged.  The psychiatrists, with Ratched present, concluded: "He's not crazy, but he's dangerous."  Ratched insists on committing Mac in spite of the danger, and her superiors defer.  Thus we see Ratched's need to win trumps good judgment.

She does win.

Mac comes within seconds of crushing her windpipe.  The ethical thing to do following the attack would have been to assign Mac to the disturbed ward or to have him released into the custody of the corrections dept.  She doesn't.  She arranges a lobotomy for Mac.  That's how she wins.  Ratched destroys Mac's ability to to function at all.  She neutralizes him.  She takes away his humanity. 

We realize at the end of the film that Mildred Ratched's means of asserting herself is to crush the souls of others.  She has beaten down the other men on the ward.  It was better for Billy to die than for her to let his soul breathe.  McMurphy saw what Ratched was in the beginning and fought it.  It took a bit longer with violence and personal injury on the way, but she triumphs over Mac too.

Charlie Cheswick (Sydney Lassick) is another patient who challenges Ratched under Mac's influence.  He is punished with a session of horrific electroshock therapy and broken back down.  Only Chief Bromden, who stayed out of the game by feigning deaf-mute escapes in the end.

Here is another exceprt from the film.  One of my all time favorite temper tantrums: Charlie Cheswick's cigarettes.

Caution: violence, strong language
http://www.youtube.com/watch?v=7D75Yub3Bds