But would you need nitro? What about something that reacts, something like an acid/alkali mix, to release smoke and nasty fumes? All the bad guys would need to say is "Next time it will go BOOM" and there you have the desired effect. (You do not want to know some of the things I have found online regarding liquids. For obvious reasons I ain't posting them here)
Makes a mockery of the "100ml" rule, when you think about it. After all, the IRA crippled a large chunk of London several years ago just by saying "There's a bomb on a District Line train" (I was caught up in it, every train was emptied ASAP at stations and the whole lot checked out. Was a hoax, of course, but it had the desired effect). Why bother making the "big bang" when you can cause enough chaos with the threat of it? There is an obvious follow on to that too.........