How is Nurse Ratched from "One Flew Over the Cuckoos Nest" Belligerent?

How is nurse Ratched belligerent? Have you seen the movie or read the book? Her character is portrayed to be a controlling, self centered, omni present, *****. She terrorizes her staff and the patients in the unit that she supervises. And yes, there are some people just like her. Personally I have known one or two that fit the script and sure hope that this personality type are small within the general populace.