Aaron, often these people don't realize that everyone can hear them. I wouldnt chuck my popcorn at them, as you could come of looking like an asshole. Best thing to do, is tap him on the shoulder and politly tell him to STFU. So he is aware that he's pissing people off. And if that doesnt work...
we pay enough for cinema tickets these days, so i don't get why they can't have some security guy in the cinema, ready to escort annoying people out of there. The trouble is it's left to other cinemas goers to tell these people to STFU, it shouldn't be our problem.