The main difference between the Cunninghams and the Ewells is the difference between what is known as "poor white" and "white trash," or, as Mammy in "Gone with the Wind" termed them: "buckra." The Cunninghams are honest and proud, albeit poor. They do not want someone to give them anything. For instance, Walter Cunningham is embarrassed by Scout's teacher's attempts to learn why he does not have a lunch, but he will accept nothing. The Ewells, on the other hand, live as a dysfunctional family in which verbal and physical abuse abounds. For, Bob Ewell is abusive and lazy; he does not repar anything around his house. When he sees his daughter making advances at Tom Robinson, he curses her and calls her names.
Yet, he does not have the decency to refrain from putting any blame on Tom; instead, he delights in doing so simply because he can and he wants to feel superior to someone, at least. No Cunningham would do such a thing. Later, Ewell even tries to harm Scout and Jem simply because they are the children of Atticus who has shown his daughter to be a liar about the "rape." Rather than being a character with ethics such as a Cunningham is, Bob Ewell is a despicable character.