Back in the 90's, my brother-in-law was going on a 1-day business trip with his bosses, so all he had with him was a briefcase. He put it on the belt for the xray machine and walked through the arch before the belt started running. He's standing there, waiting for his briefcase to come through. The belt stops and the person running the scanner calls over his boss.
Scanner: "Is this what I think it is?" Boss: "Well, what do you think it is?". Scanner: "I think it's a gun." Boss: "Well, it looks like a gun to me, too." My BIL thought Boy, someone's in big trouble until he realizes that his briefcase was still in the scanner.
The belt starts up again, out comes his briefcase and the scanner says, "Sir, is this your case? Would you please open it?". BIL opens the case and sure 'nuff, there's a gun in the briefcase.
He said he thought he was going to pass out. He starts sputtering, "That's not my gun! I didn't put a gun in my briefcase! I don't know how that gun got in there!", all the while picturing that within seconds he would be on the floor with an armed guard standing on his neck. Then the boss steps forward and says, "I know you didn't put that gun in there. I put the gun in there for a test." Apparently, as soon as my BIL put his case down and stepped through the arch, the boss flipped the case open and put in a non-functioning test gun in the case.
It's a darn good thing that my BIL didn't have a bad heart (or a nervous bladder). It seems like it was a rather ill-thought-out thing to do to an unsuspecting passenger. Surely they could have used airport employees to run a test like that.
I'm pretty sure TSA didn't exist back then, but stupidity sure did. And now my BIL will never walk away to go through the arch until he sees his bag disappear into the tunnel.