Affably Evil: Mrs. Tingle. Although she's definitely the antagonist it's debatable if she could truly be called a villain.
Designated Hero / Designated Villain: Up to Eleven. On the "hero" side of the spectrum, you have 3 teens who decide to cheat on a test, and are caught by the "villain." They then go over to her house, break in, kidnap her, knock her unconscious (albeit unintentionally), tie her to her bed, attempt to blackmail her by taking staged incriminating photos of her committing adultery, and finally changing one of their grades from a well deserved C to an A+, and another girl's well deserved A to a B. On the "villain" side, she insults some people, admits she resents all her students, and is cold and distant.
Mrs. Tingle isn't the only Designated Villain, either. Another girl in the class is demonized because...she gets better grades than the protagonist?
Jerkass Woobie: Mrs. Tingle. Again, it's the kids who barge into her house and threaten her then tie her up.
Rooting for the Empire: It is very easy to find yourself rooting for the supposed villain of the film, Mrs. Tingle, who is probably the most sympathetic character in the entire film.
Strawman Has a Point: The title character is a high school Sadist Teacher who has it in for the lead character, who is just trying to become valedictorian. At the start of the film, Mrs. Tingle gives a C grade to a project she worked six months on, a historical recreation of the diary of a girl accused of being a witch during the time of the 1692 Salem Witch Trials. Except that the diary describes witch-burnings, whereas the accused witches at Salem were all hanged, except for the one man who was crushed, meaning the teacher was well within her rights to mark the assignment down.
On an even bigger note, one of the kids brings a medieval crossbow as a school project (his reasoning being he wants to be a cop when he grows up.). The crossbow goes off and almost hits somebody. Mrs. Tingle calls him an idiot, which we are supposed to think is horrible even though she is completely right!
What an Idiot: Once Mrs. Tingle freed herself, all she had to do was call the police and the situation would've been throughly handled. Instead, she calls the school and tells the principal to come down to her house, because the cheating was apparently more important than the kidnapping, blackmail and assault and THEN tries to kill Leigh Anne, when she knows the principal is on his way.