What causes Jem to wreck Mrs. Dubose's camellias in the novel To Kill a Mockingbird?

In Chapter 11, Jem and Scout are heading to the store to spend his birthday money, when Mrs. Dubose begins to verbally insult them. She accuses the children of playing hooky, even though it's Saturday, and tells Jem that Miss Maudie told her that he broke her scuppernong arbor earlier that morning. Mrs. Dubose then begins to yell at Scout for wearing overalls and says she'll grow up waiting tables at the O.K. Cafe. Jem...

In Chapter 11, Jem and Scout are heading to the store to spend his birthday money, when Mrs. Dubose begins to verbally insult them. She accuses the children of playing hooky, even though it's Saturday, and tells Jem that Miss Maudie told her that he broke her scuppernong arbor earlier that morning. Mrs. Dubose then begins to yell at Scout for wearing overalls and says she'll grow up waiting tables at the O.K. Cafe. Jem encourages Scout not to let Mrs. Dubose bother her and tells Scout to hold her head high. As they are walking away, Mrs. Dubose says, "Not only a Finch waiting on tables but one in the courthouse lawing for niggers!" (Lee 135). When Jem hears the comment, he stiffens up. Mrs. Dubose's insult "hit home" and she knew it. She then says, "Your father's no better than the niggers and trash he works for!" (Lee 135). Jem is loyal to his father and is highly sensitive to any insult directed towards Atticus. Jem takes Mrs. Dubose's insults to heart. Scout says that Jem turned red with anger, and he didn't crack a smile when he bought his steam engine and Scout's baton. On their walk back home, Jem loses his temper and destroys Mrs. Dubose's camellia bushes with Scout's new baton.