When Bob Ewell accuses Atticus of being too proud to fight, what does Atticus say in reply?

In Chapter 23, Scout retells Miss Stephanie Crawford's account of how Bob Ewell approached Atticus outside the post office. Miss Stephanie said Bob cursed at Atticus, spat on him, and then threatened to kill him. According to Miss Stephanie, Atticus didn't bat an eye and simply wiped the spit off of his face with his handkerchief. Bob Ewell continued to curse at Atticus and said, "Too proud to fight, you nigger-lovin' bastard?" (Lee 134). Atticus responded by saying, "No, too old" (Lee 134). Atticus's calm response shows his tolerant demeanor. Following Atticus's run-in with Bob Ewell, Scout and Jem begin to worry about their father's safety. Atticus then explains to them that Bob Ewell had to have some kind of comeback, which was why Bob spit in his face. Atticus tells Jem and Scout that Bob had to take his anger out on someone and that Atticus would rather it be him than Mayella or her siblings.