I'm feeling slightly lazy - so rather than try to explain the basis of the stories that make up the film here's an excerpt from the festival guide. I think overall it's pretty accurate,
With an offbeat sense of humor and an uncanny talent for observing the curiosities of interpersonal communication, Involuntary interweaves several parallel plotlines linked by the theme of group dynamics and the urge to overstep taboo. Two teenage girls chat, take pictures, and get drunk; a group of young men experiment with sex; a righteous grade school teacher tries to resolve the problem of a student bullied by another teacher; and a bus driver holds a group of passengers prisoner. In instances where characters face moral dilemmas about speaking up or staying silent, the protagonists often behave illogically to keep from losing face and find themselves in even more complicated situations. Their unpredictable behavior is reflected in the unconventional camerawork and points of view. Writer-director Ruben Östlund’s knack for perverse comedy leaves the audience with questions about lessons to learn, lectures to give, and lines not to cross.