I think I'd wait until an attack seemed imminent, although I might've gone into the bathroom immediately after they had exited it. Not sure what sitting next to one would do, though...
Hopefully siting next to one of them would have precipitated an argument which would have caused the plane to land. Undoubtedly this would have gotten me in trouble with the authorities but a) I'm not taking any chances at that point b) I would go public so fast your head would spin.