“Bad Teacher” aims to be the sister comedy to 2003's "Bad Santa," another one-joke, R-rated premise about supposedly kid-friendly people hating and cursing out kids, with hints of the more lighthearted “School of Rock” thrown in. But “Bad Santa” went all the way with its indecencies, and had an actual plot framed around them. And in “School of Rock,” the joke was that Jack Black’s teacher was the child, learning to shed his ego through his students’ sweetness.