Humm, kind of reminds me of my brother who has a horrible habit of laughing when something like this happens. It is just a nervous laugh but he laughs none the less. I am always very worried he is going to get the shit beat out of him one day, if he starts laughing with the wrong person.
I remember seeing the porn shoot when the camera man got a facial being in the wrong place at the wrong time. It was really funny and everyone on the set started laughing. Then there is always the poor guy getting hit in the nuts that, always incites a good laugh.