In The Gift of Fear, Gavin de Becker talks about how, as a security consultant, he takes offhand jokes very seriously. He tells the story about the office which

In The Gift of Fear, Gavin de Becker talks about how, as a security consultant, he takes offhand jokes very seriously. He tells the story about the office which received an odd-looking package that nobody was expecting. They debated whether to open it. Eventually one guy decided to open it, so his coworker left the room. As the coworker was leaving, he made an offhand joke over his shoulder: "I'm going to stand in the other room so I won't be around when the bomb goes off." Then the bomb went off. Jokes are designed as a mechanism for saying speculative, potentially scary things without being threatening or looking stupid. When I see a TSA agent with that wallpaper, I see someone who knows at some level that something is very wrong but isn't able to say so out loud. Maybe they can't even say it out loud to themselves.