Perhaps, the Acutes resent McMurphy in Kesey's One Flew Over the Cuckoo's Nest because he demonstrates the manliness that they lack. For instance, Billy Bibbit is emasculated by his mother, Harding by his young, pretty wife. Bromden has become weak like his father who was made "smaller" by his wife. As another example, he beats them at cards so much that they must write IOUs to cover their bets. And, while they allow Nurse Ratched to emasculate them through insinuation, intimidation, and manipulation, McMurphy opposes her through acts of independence such as his refusing to be defeated in his loss on the vote to watch the World Series on television.
Further, McMurphy's mental strength acts as a constant reminder to the others that they have admitted themselves to the institution because of their lack of masculinity. In Chapter 11, for example, McMurphy bets the others that he can heave a control console weighing around 400 pounds through the wired window and escape. Although he cannot lift this control panel, he still causes the concrete to "groan" some. More importantly, he at least makes an effort, refusing to accept defeat before beginning as they have done regarding the viewing of the World Series: "But I tried, though...." he tells the men as he reliquishes to them their many gambling IOUs.
Indeed, McMurphy's indomitable spirit is a constant reminder to the Acutes of their weakness and pusillanimous natures. As Bromden characterizes McMurphy, his aplomb is apparent:
But McMurphy can't keep still for that [Nurse Rached tells the men to be still or watch the clock]; he's got to be up to something. After about two minutes of pushing food scraps around his plate with his spoons, he's ready for more excitement.
Unlike the other men, McMurphy proves a worthy adversary for the cruel and controlling Nurse Ratched. And, when they view him, the Acutes perceive what they lack.