By Roger Ebert
“Bad Teacher” immediately brings “Bad Santa” to mind and suffers by the comparison. Its bad person is neither bad enough or likable enough. The transgressions of Elizabeth Halsey (Cameron Diaz) are more or less what you’d expect, but what’s surprising is that she’s so nasty and unpleasant. Billy Bob Thornton, as the Bad Santa, was more outrageously offensive and yet more redeemed by his desperation. He was bad for urgent reasons. Elizabeth seems bad merely as a greedy lifestyle choice.
As the film opens, Miss Halsey is engaged to a rich guy she leeches on but doesn’t love. She’s dumped and has to return to teaching, an occupation she had no talent for or interest in; she passes the time showing DVDs to her students while she naps, drinks and does drugs at her desk. This creates astonishment and indignation in the charmingly named Amy Squirrel (Lucy Punch), whose classroom is right across the hall.