As I said before, Bruce, the simple solution to that problem -- the one that would cost the airlines the least and screw up the travellers' lives the least -- would be to put all carry-on liquids into LOCKED overhead bins.

Of course, you could also prohibit passengers from carrying anything but a wallet into the lavatories.   (Although the instructions for mixing your explosives in the john do make you wonder how feasible that would be.) And I'd think someone trying to mix explosives in their seat would trigger a lot more attention than someone trying to set a match to his shoe.