I'd just like to say that when faced with other peoples misfortune the humans have a physiological reaction of laughter or a sharp laugh - like when you get nervous, you laugh at stupid shit. Its an involuntary reaction and its actually a sign of relief that the misfortune hasnt happened to them, bear in mind its an involuntary physiological reaction.

This is played on by good comedians and is generally why people laugh at some really sick stuff sometimes