In Chapter 26, Miss Gates lectures her students about what constitutes a democracy. She says that America, unlike Germany in the 1930s, is a democracy, and this is because Americans "don't believe in persecuting anybody." She explains that "persecution comes from people who are prejudiced." She tells the children that the persecution of the Jews by Hitler and the Nazis is a hateful and deplorable act. Miss Gates also points out how irrational the persecution of the Jews is when she says that Jews "contribute to ... society" and "are a deeply religious people."
Later in the same chapter, Scout tells Jem that she overheard Miss Gates, "coming out of the courthouse" after the trial, saying to Miss Stephanie Crawford that it was "time somebody taught 'em a lesson," and that "they were gettin' way above themselves, an' the next thing they can do is marry us." The "they" that Miss Gates refers to so contemptuously are African Americans, and the "us" is of course white Americans, specifically white women.
Scout astutely points out the irony, or hypocrisy of Miss Gates's views when she asks, "how can you hate Hitler so bad an' then turn around and be ugly about folks right at home." Miss Gates's views are ironic because they are contradictory. She is deeply critical of Hitler and the Nazis for irrationally persecuting the Jews in Germany. At the same time she is, hypocritically, complicit in precisely the same kind of irrational persecution of African Americans in her own country. She is one of the ignorant, "prejudiced" people that she was critical of in her own aforementioned lecture. It is also deeply and tragically ironic that Miss Gates seems to be utterly oblivious to her own hypocrisy.