Prejudice is a horrible and unfair thing, but unfortunately, almost everyone has experienced it at some time in their life. It's a main theme in To Kill a Mockingbird. Almost everyone has judged someone before getting to know them; the people of Maycomb seemed to do it all the time. There is prejudice throughout the whole story.
In Maycomb, everyone had heard stories of "Boo" Radley. Children feared him; most adults tried not to speak of him too much, but no one actually knew him. The children in Maycomb thought he was a viscous monster, a man with a scar on his head and bloody hands and who ate cats and squirrels. The adults thought he was crazy, and that they kept him in that house because he killed his father with scissors. People were afraid to even go near the Radley house because of what they thought lived inside of it. No one knew that in reality, Arthur "Boo" Radley was not a monster, just a man that never really grew up and didn't like to be in public too much. .
In the 1930's, where To Kill a Mockingbird was set, it was not considered "proper" for a young lady to dress in overalls and participate in the same activities that boys did. Jean Louise Finch (Scout) did just that, and as a consequence was prejudged by the ladies of Maycomb, except for Miss Maudie. Women like Mrs. Dubose would always criticize her about how she acted, saying things like "Don't you say hey to me you ugly girl!" People thought of Scout as a little tomboy who wasn't doing or acting like what girls were supposed to, and they tried to change her without really looking past appearances.
Even Scout herself is guilty of being prejudiced. For example, Scout heard a lot of the stories about Boo Radley, and she was always making plans with Jem and Dill and trying to figure out ways to see him. She really believed that he was the monster depicted in the stories she heard. Then a little later in the story, she starts to learn about what Boo is really like, and by the end she realizes that he is just a child in a man's body.