When does the book To Kill A Mockingbird by Harper Lee say that Bob Ewell is "trash"?
Scout tells Calpurnia that her father referred to the Ewells as trash.
The Ewells are white, but they are also very poor. Their ignorance and refusal to get an education annoys Atticus. Atticus is usually very understanding of people, but he makes disparaging statements about the Ewells.
“Mr. Ewell?” My memory stirred. “Does he have anything to do with those Ewells that come every first day of school an‘ then go home? Why, Atticus said they were absolute trash—I never heard Atticus talk about folks the way he talked about the Ewells. He said-” (Ch. 12, p. 164)
Atticus does not approve of the Ewells because they only bring their children to school on the first day and then keep them out after that. Bob Ewell is also an alcoholic who drinks away his relief checks instead of using them to pay for food for his expansive brood. As a result, the law looks the other way when he hunts out of season.
Atticus also does not approve of where and how the Ewells live. They live near the dump, in a very decrepit shack.
They were people, but they lived like animals. “They can go to school any time they want to, when they show the faintest symptom of wanting an education,” said Atticus. (Ch. 3, p. 40)
Atticus puts the lifestyle of the Ewells in full view during the trial of Tom Robinson. Mayella Ewell accused Tom Robinson of rape, but Atticus proves that it was Bob Ewell who hit her, and that he regularly abused her before the rape allegation. Ewell is greatly insulted, feeling that his reputation was ruined and it was all Atticus’s fault.
The Ewells are at the bottom of Maycomb's food chain, except for the Robinsons. Since they are white, that still gives them more credibility and status. Racism is an unavoidable way of life in Maycomb.
Note: Page numbers vary by edition, these are from the Fiftieth Anniversary Edition.