IEEE Spectrum: Unsafe At Any Airspeed?: "In one telling incident, a flight crew stated that a 30-degree navigation error was immediately corrected after a passenger turned off a DVD player and that the error reoccurred when the curious crew asked the passenger to switch the player on again. Game electronics and laptops were the culprits in other reports in which the crew verified in the same way that a particular PED caused erratic navigation indications."
It's merely annoying when someone's cell phone goes off in a theater or a classroom. But any numbskull who ignores the warnings of flight attendants ought to have his/her thumbs broken with a hammer.