In Part Two, McMurphy is shocked to learn from Harding that Scanlon is the only patient besides him who is involuntarily committed to the mental hospital. There is situational irony at play in this exchange:
“You have more to lose than I do,” Harding says again. “I’m voluntary. I’m not committed.”
McMurphy doesn’t say a word. He’s got that same puzzled look on his face like there’s something isn’t right, something he can’t put his finger on. [Harding] swallows and says, “As a matter of fact, there are only a few men on the ward who are committed. Only Scanlon and—well, I guess some of the Chronics. And you. Not many commitments in the whole hospital. No, not many at all.”
In Part Three, Bromden wants to sign up for McMurphy's fishing expedition but is afraid to do so because of the dramatic irony he has maintained so long around his hearing. He is amused by the situational irony:
Unlock with LitCharts A+[I]t’d show I’d been hearing everything else that’d been said in confidence around me for the past ten years. And if the Big Nurse found out about that, that I’d heard all the scheming and treachery that had gone on when she didn’t think anybody was listening, she’d hunt me down with an electric saw, fix me where she knew I was deaf and dumb. Bad as I wanted to go, it still made me smile a little to think about it: I had to keep on acting deaf if I wanted to hear at all.