I do this at the most inappropriate times, but I have to be so severely overloaded emotionally that I don't have the capacity to respond correctly.
I remember one day...I'd just had a fight with my boyfriend, I'd been yelled at at work, I received a bad grade on a test and was in danger of flunking the course, and when I came home my mother told me my father was in the hospital.
I started laughing.
She was flabbergasted. "You think this is FUNNY?" (ESTP Mom). I told her of course it wasn't. But this was just the topping on the stressful cake. I literally did not have the capacity to do anything else *but* laugh.