Men traveling by themselves with practically no luggage seem to irritate the American authorities. It’s not so much that they think you are a drug trafficker as that you fit, in the most schematic possible way, the profile of the most pathologically optimistic conceivable drug trafficker, and hence practically force them to investigate you. Irritated that you have forced their hand in this manner, they want to teach you a lesson: travel with a wife and four kids next time, or check a few giant trundling bags, or something, man! What were you thinking?