What happened when Bob Ewell meeting with Atticus at the post office?

When Bob Ewells met Atticus at the post office he spit in his face, called him names and asked him "Too proud to fight, you 'African American' lovin' *?" Atticus just walks away. Atticus later tells Jem and Scout not to worry about it because Mr. Ewells just needed to get out his frustration about his reputation being hurt by the trial.