Films with time-traveling bears tend to defy easy description. So do movies where a teenager has alien fly mutant blood and was forced to wear a TV set on his hand as a child. It’s also tough to describe a flick where a Ghostface-like slash wanders into the picture and isn’t the focal point. Director Joseph Kahn has swirled all these elements and more into the delightful, abrasive lunacy of his new film, Detention. The movie is a rapid-fire assault on the senses, and while it plucks at your neural pathways like an inbred hillbilly armed with a banjo and amphetamines, Kahn’s picture has sharp mind, a charming wit, and a scathing critique on nostalgia and the narcissism of teenagers both past and present.