A school class waits to be dismissed for a summer vacation. Before that, all have to endure their teacher's slide show. There's still time for one harmless prank.A school class waits to be dismissed for a summer vacation. Before that, all have to endure their teacher's slide show. There's still time for one harmless prank.A school class waits to be dismissed for a summer vacation. Before that, all have to endure their teacher's slide show. There's still time for one harmless prank.