What isn't unusual about McMurphy? The word "unusual" takes on a much different meaning in a mental institution. I spent the first half of the book just trying to decide whether he was truly mentally ill or not. Or whether many of those inside were. Clearly, some of his compatriots needed to be institutionalized, but McMurphy was a match for Nurse Ratched, and the others enjoyed watching them go back and forth, with McMurphy winning a good deal of the time. If he did have mental issues, they didn't affect his intelligence or awareness of himself and those around him.
His voice and laughter were commanding, they had a presence that gained attention, both positive and negative from those around him and the hospital staff.
McMurphy in the book One Flew Over the Cuckoo's Nest is a unique individual. He has a loud boisterous laugh and worn hands that look like the hands of a laborer. When the other patients hear him laughing they are puzzled at first, but the more that they get to know him the more his laughter brings out their laughter.
McMurphy is in the place because he though if he acted like he was crazy he could go there, no have to work, ad get out soon. He has the basic personality of a person who likes to combat rules and authority but does it in a laughing mischievous way.
Nurse Ratchet identifies his anti-social behaviors and finds a worthy adversary in him. She wants to break him down at all costs so that she does not lose face on her ward.
He is actually the sanest inmate of the hospital and wants to help his fellow inmates have fun