McMurphy's Committal to a Mental Institution (Situational Irony)
The fact that McMurphy is committed to a mental institution is itself an example of situational irony, because he has committed a crime but exhibits no signs of insanity. McMurphy cons his way into being committed to the hospital, because he believes it to be a lighter sentence than a prison farm. However, his committal to the hospital serves to only drive him more insane, as he feels confined and limited by the structures that determine his life there. The situational irony exists in the misalignment between McMurphy's expectation and the reality of his situation and its outcome.
The Patients Have the Choice to Leave but Do Not (Situational Irony)
McMurphy becomes completely disturbed and shocked by the irony that while he is committed to the institution indefinitely, many of the men who stay there are staying of their own will and are free to leave whenever they choose. McMurphy can only dream of freedom from the hospital, but so many of the others choose their own confinement. McMurphy cannot wrap his head around this irony and it eats away at him. His expectation that no man would choose captivity does not line up with the reality that many of the men have in fact chosen to stay in the hospital.
Chief Bromden Can Hear and Speak After All (Situational Irony)
The entire first half of the movie leads the audience as well as the other patients to believe that Chief Bromden is completely deaf and mute and unable to comprehend most of what is going on around him. This plays into not only a plot device, but also a cultural stereotype about the imposing, silent, and dim American Indian chief. The irony is that while Chief seems like one of the more prohibitively insane patients, when he speaks he is revealed to be completely lucid and responsive, and one of McMurphy's most sane allies. The situational irony, therefore, is that while we (like McMurphy and the others) expect the Chief to be deaf and mute, our expectation is completely reversed when he is able and willing to hear and speak.
The Doctors in the Disturbed Ward (situational irony)
Nurse Ratched is the nurse for the milder cases of mental instability, and yet she is the most hard-nosed and imposing nurse in the hospital. The nurses and doctors for the more severe cases in the hospital are much gentler and less manipulative than Nurse Ratched. There is situational irony in the fact that Nurse Ratched does not need to be as strict as she is, but she insists on running her ward as though it were a prison, while the doctors who might reasonably be expected to be stricter and administer more violent procedures seem kinder and more measured. The viewers' expectations for what ought to be the case are reversed.
