How would you describe Bob Ewell's attitude on the witness stand? What reasons might he have for acting this way?

Bob Ewell's attitude on the witness stand is challenging and disrespectful of the law, as evidenced by his inflammatory use of the word "rape" to describe what he claims he saw Tom Robinson doing to his daughter and his attempts to play with language during a serious law proceeding.
At this point in time, the word "rape" was not a word heard in conversation amongst polite company, and Bob uses the shock value of this word to alarm and upset the people of Maycomb watching the trial. As well, by using such harsh language to accuse Tom out loud in a court of law, he is attempting to manipulate the system but setting up a negative feeling towards Tom that is impossible to undo.
Once Bob has seen the horrified reaction of the people in the courtroom, Bob is ready to get off the stand, so he is unprepared for Atticus's questioning. He is suspicious of Atticus, but Bob thinks he can outsmart him and he tries to amuse his audience. When Atticus shows that Bob is left-handed, Bob gets very angry and claims that he is the one who has been taken advantage of, speaking out of turn to the judge and revealing Bob's overall disrespect of Atticus and the trial itself.
Bob may have acted this way out of his anger and resentment towards Atticus, who is educated and better-off, or he may have acted this way to try and distract others from his role in his daughter's suffering. Perhaps Bob feels like he rarely has an audience, and because he doesn't get much attention, he couldn't help himself when he was trial and he did everything he could to get even more attention. Whatever Bob's reason, the fact of his disrespect remains.