Del Griffith's declaration that he knows what kind of person he is, and he's not going to change. It's clearly John Candy himself talking as much as the character, and easily the most moving scene of his far too short career.
After Neal's long f-word-filled rant, the clerk played by Edie Mc Clurg calmly asks him if he has his rental receipt. His response? "No, I threw it out." She responds awesomely: "You're fucked."