It seems to me that whatever your emotional reaction is, then that's your reaction and at the moment there's really not too much you can do about it other than try to calm yourself. I would say that the most important thing is making sure that your emotional reaction doesn't get in the way of the rest of your game.
In other words, if crying helps you get the bad beat off your chest, and your head back in the game, then by all means cry your eyes out. Then get back to playing poker. If, however, you find that crying puts you in a bad space where you start tilting and spewing your chips until you've got nothing left but felt, then you'll want to find a way to stop those tears from flowing. Maybe a song you can listen to on your iPod, or a phrase you can repeat in your head or out loud. Perhaps you can try and remember a good time in your life or the time you took down a huge pot.
Hope that's helpful!