If it's what I'm thinking of, it's highly offensive and distressing, involving a government conspiracy, a high-profile incident, and a picture that appears to show the same person before and after the incident. Even if it's not what I'm thinking of, it's probably something else that makes the OP wonder "what the ...."
I really don't think there's a way to ask a grown person if he or she is serious. Just let it roll off and ignore it. I know, harder to do than say, but I think that's the path of etiquette.