You have to have some emotional distance to be able to laugh or tell a joke about a disaster. I haven't yet talked to a person who didn't know someone who numbered amongst the 5.000 or so people who died on Sep 11th. I don't think most people who DO have that distance are telling jokes, because in effect, they're most likely telling them within earshot of someone who hears the screams of a loved one echoing in their nightmares.