In Chapter 18, Mayella Ewell takes the stand to testify. When Atticus begins his cross-examination, he refers to Mayella as "ma'am." Mayella has never had anyone speak to her politely before and takes offense to Atticus's courteous remark. Mayella tells Judge Taylor that she refuses to answer any questions as long as Atticus continues to mock her. Judge Taylor seems confused as to why Mayella has taken offense to Atticus calling her "ma'am," and she insists that Atticus is giving her sass. Despite being known as a strict man who never evokes pity, Judge Taylor explains to Mayella that Atticus is simply being courteous. Mayella is not used to people treating her politely because she rarely leaves her home. Unfortunately, Mayella Ewell has no friends and her father is an abusive alcoholic. She was not raised in a loving home where people treat each other with respect, which is why she misinterprets Atticus's gesture of courtesy.
Mayella gets very upset and begins to cry hysterically when questioned by Atticus. She angrily accuses him of making fun of her by using the term "ma'am" when speaking to her. She is obviously not used to people treating her with respect or kindness.
Even in the courtroom, Atticus is always a gentleman. When he questions Mayella, he is polite and kind. Mayella has never been spoken to in this manner. She is only familiar with her father's harsh and often crude talk, as shown every time he speak. Therefore, when Atticus uses his manners in the courtroom, Mayella thinks he is making fun of her. She doesn't know what manners are because she has never heard them or spoken them. She led a rather isolated life with her father as the only adult influence. Naturally, when he speaks to her in a rough manner, that's all she expects of others. To be spoken to gently and politely is foreign to her.