The entire exchange between Catherine and her father after Morris stood her up. The best parts:
Catherine: Don't be kind to me; it doesn't become you.
Catherine: You have cheated me! You thought that any handsome, clever man would be as bored with me as you are were. It was not love that made you protect me—it was contempt!
Dr. Sloper: You have found a tongue at last, Catherine. It is only to say such terrible things to me. Catherine: Yes. This is a field where you will not compare me to my mother.
Dr. Sloper: Promise me you are done with him! Catherine: I won't promise. Dr. Sloper: Then, I must alter my will. Catherine: You should... you should do it immediately!
Dr. Sloper: I don't want to do it. I don't want to disinherit my only child. Catherine: You'd like to think of me sitting in dignity in this handsome house—rich, respected and unloved. But I may take your money and chase after Morris and squander it on him. Dr. Sloper: I don't know what you would do, Catherine. Catherine: That's right, father. You'll never know, will you?
Catherine's treatment of Morris at the end of the film is beautifully done and it illustrates just how far she's come from the timid, awkward girl she was at the beginning. While the younger Catherine was so desperate to be loved that she put up with all kinds of cruelty, the older Catherine is wiser and more self-assured. The entire scene with Morris desperately pounding at the locked door as Catherine walks away is the definition of awesome when you think of how codependent she was before.