At the end of chapter 22, the reader is told that Bob Ewell spit in Atticus's face and "told him he’d get him if it took the rest of his life." Then the chapter ends.
Chapter 23 starts up and Atticus says, “I wish Bob Ewell wouldn’t chew tobacco.” The rest of the event is summarized by Miss Stephanie Crawford, who saw the exchange take place. Miss Crawford explained that
"Atticus didn't bat an eye, just took a handkerchief and wiped his face and stood there and let Mr. Ewell call him names wild horses could not bring her to repeat."
Mr. Ewell then asked Atticus if he was too proud to fight. Atticus responded by saying that he was too old, put his hands in his pockets and walked away.
Atticus's response was that he didn't react. It shows a great strength of character in Atticus. He can't be goaded into a fight easily. It shows that Atticus is extremely confident. Hurtful words spoken by a drunk and violent man are easily shrugged off by Atticus. It's a cliche, but sticks and stones could hurt Atticus, but words definitely do not hurt him in this instance. The incident also reveals that Atticus has great control over himself and does not have a quick temper.