Only when things get REALLY unbearable for me. Like unbearable anger, pain, sadness, etc. I don't usually show it to other people, but I did have my moments.
On the lighter side, I do cry during scenes of unbearable emotion (i.e when mufasa died in lion king haha). Even some romantic teen comedies make me cry.
I'm a very...uhhh...empathic person i guess, I get swayed by strong emotions easily. :P