On a recent trip to the U.S., a friend gave me a book that I had ordered on Amazon and had delivered to her apartment. (Amazon sends books to Mexico but shipping charges are whoppingly expensive. So when I'm in the States I try to have books sent to people I know and then pick them up.)
I suppose it was a bad idea to leave the book in its shipping box unopened. I never do that, but this was an art book, and I wanted it to arrive undamaged. In any case, the TSA thought something fishy was going on, and before my flight home, examined my luggage top to bottom. They burrowed around my suitcase, finally opening the package to find nothing more life-threatening than printed matter. They included a circular that made it clear they had been through my belongings.
The officer who did the inspection must have had other things on his mind that day, because when he finished giving the once-over to my boxer shorts, dirty laundry, dental floss and so forth, he left his Master Mechanic box cutter inside the suitcase. I now possess a powerful weapon. Did he even notice it was missing? Are there plenty more where it came from? People in the U.S.: these are your tax dollars at work.