I personally know someone who was detained at CVG for making such a joke. He was trying to be "cute" with the semi-attractive gate agent by making a gun joke. The conversation went something like:
GA: Hello sir.
Larry: Hi there! Is this where I check my gun?
GA: You are saying you have a gun???
Larry: Lemme check....Nope just happy to see you!!
In the meantime he boards and the agent talks to her supervisor. LEO is called and Larry (not his real name) is escorted from the plane and taken into an interrogation, errr....i mean "interview" room. He is kept there for almost 6 hours before being cut loose and forced to catch a flight the next day.
While this behavior is stupid and annoying I don't think it should be grounds for FBI intervention. The words "gun" and "bomb" and countless others are part of our language. How many times have you ever heard a young hipster say something is the "bomb"? Should this be grounds for detainment? I'd say no. TSA and airport personnel should be trained to spot credible threats. The real focus should be on repairing all the holes in our "Homeland Security." Then again, harassing harmless passengers and instilling fear might just be part of our re-education as a society.