In many instances in this novel, you can tell what a character’s personality is like based on their physical appearance. For example, McMurphy has tattoos, which might lead you to believe he’s a bit of a rebel. Kesey often describes Nurse Ratched as having a face that looks like it’s made of plastic, so she’s pretty much a fake and inhuman. Doctor Spivy is scrawny, has tiny eyes, and wears glasses, so he’s a pushover.
The way characters dress provides insights into their personalities. Nurse Ratched’s perfectly white, tight uniform indicates her obsession with cleanliness and order as well as her attempt to contain her womanhood by disguising how big her breasts are. McMurphy, in contrast, is often wearing boxers with whales on them, showing that he’s quite a bit more free-spirited.
In this novel, you can usually make broad generalization about characters based on their occupation within the ward. For example, the orderlies are there to keep the patients in line and to enforce rules and regulations. By default, this makes them mean people. This places them in a position of authority over the patients, which allows them to abuse their powers.
Within the book, the patients have a system of categorizing each other. The Acutes are more mobile and active and able, if pressed, to think for themselves. They also tend to be voluntary patients, showing that most of them are there because they’re afraid of the outside world. The Chronics are patients that aren’t expected to ever be able to leave the ward. Most of them were committed to the ward, so they aren’t voluntary patients. For the most part, the Chronics also are so ill – or so damaged from treatments like lobotomies – that they can hardly even move around or understand anything that’s going on around them. The only Chronic that doesn’t fit the mould is Chief.
McMurphy is up on current slang and he uses it constantly. For example, he calls prostitutes "twitches" and refers to the other patients as "birds" as in "You birds want to wager a bet?" McMurphy’s style of speech is important because it further emphasizes that he’s a man of the Outside world and that he’s a free spirit. Unlike the stodgy and dated speech of many of the other patients, McMurphy doesn’t sound like he’s been stuck in an insane asylum for 10 years – he sounds fresh and lively.
Some of the patients speak in a really stiff way. The worst offender would definitely be Harding. He says things to McMurphy like, "A ‘pecking party’? I fear your quaint down-home speech is wasted on me, my friend. I have not the slightest inclination what you’re talking about." Wow. Harding definitely sounds like he’s been locked away for a long time, especially in contrast to McMurphy.