Bad Teacher is a bad movie. Very bad. It's supposed to be a comedy, but it's not funny.
It may not be fair to compare it to Bad Santa, but I'm going to anyway. Both movies are about bad people who have a job that requires someone with a certain amount of decency. When you take your child to see Santa at the mall, you would be horrified if a drunk criminal was working as Santa and yelled at your kid. You also hope that the people who teach your kids are interested in providing them with a decent education.
Billy Bob Thornton was perfect for the role in Bad Santa. Cameron Diaz is miscast as the Bad Teacher. She plays mean really well, but unlike Thornton, she isn't any fun to watch in this role.
Also, in Bad Santa, Thornton's motivations made sense. He was a thief, and found that by working as a Santa in a store, it gave him an advantage when it came time to rob the place. He wasn't necessarily mean to kids because he hated them, it was just because he could care less about doing the job well. As soon as he robbed the store, he was out of there. In Bad Teacher, there isn't any reason for Diaz to act the way she does. It doesn't make sense that she is such a horrible person.
When the movie opens, we meet Elizabeeth Halsey (Diaz). It's the last day of school at John A. Adams Middle School. It's also Miss Halsey's last day. She has only been teaching there a year, and she is about to get married to a rich man. So she is retiring, since she won't need the money any more. When her fiance dumps her for being a gold digger, she has to go back to work.
The movie doesn't really address whether she was a bad teacher the first year or not. When the principal is giving her a going away present, she certainly seems pleasant enough. But after being dumped, she is pissed off and bitter. This doesn't really make sense. She admits that the only reason she got into teaching in the first place was because of the hours and summers off. It's hard to believe that someone who hates teaching so much would get through all the college and student teaching you have to do.
Since she isn't interested in teaching, all she does in class is put a movie on while she sleeps. She's like the laziest substitute teacher you ever had, but she's your regular teacher. For whatever reason she chooses inspirational movies about school (Stand and Deliver, Lean on Me), and while the movie plays she sleeps or drinks from the little liquor bottles she keeps in her desk.
She seems to have two motivations in this movie. The first is to find and marry a rich man. The second is to get breast enhancement surgery, which will cost $10,000 that she doesn't have. This doesn't make that much sense, as she already looks like Cameron Diaz and has no trouble getting guys to like her. Except for one guy, played by Justin Timberlake. JT plays a substitute teacher who for some reason starts teaching there full time. This isn't explained, but I digress. JT's grandfather designed fancy watches, and so Elizabeth decides to go after him. She never does ask him about his finances. Just because his grandfather made watches doesn't mean he is rich. But again, I digress.
There are subplots that don't go anywhere. When she hears how much money the school benefit car wash raised, she decides to be in charge of the next one. She dresses in cutoff shorts and a skimpy top, and the car wash is a success. We see her afterwards counting her money, so we know she kept some of it for herself. But we also hear the principal say that the car wash brought in $7,000. Did she give the school $7,000 and keep more for herself? How much? Or did she tell him it raised $7,000 and just keep it all? The movie never explains. And if the car wash is so lucrative, why doesn't she just keep doing car washes? She would have her new boobs in no time.
Another idea she has is to get the students' parents to pay her for supplies and tutoring. She guarantees them an A in her class, or their money back. None of these parents stop to think that since she is the teacher, she is the one who decides their grades. But the movie never follows up on this. We see the parents give her money, and it isn't mentioned again.
None of the kids are developed as characters, and they have very little screen time. We get to know a couple of the kids a little bit. One girl is a teacher's pet. She dresses prim and proper, and her mother bakes cookies for her to bring to the teacher. She doesn't seem too bothered by Elizabeth's attitute towards her. The other kid is a shy boy who writes poetry and has a crush on a pretty girl in his class.
There are some funny actors in the cast, but they are given nothing to do. The only one who gets any laughs is Jason Segel, and he isn't given much to do either. He plays the gym teacher, and he is always hitting on Elizabeth. She keeps turning him down because he's a poor teacher, but he keeps persisting. His character seems smart, yet he isn't smart enough to recognize she's a gold digger. Or he just doesn't care.
This script is just horrible. It was written by Gene Stupnitsky and Lee Eisenberg, who wrote the awful Year One. I pray to God that their script for Ghostbusters 3 never gets made.