A Phony IED
One of the passengers on this flight was going to explosives detecting training exercise. Since it was an inert IED, he should have known better than to walk through a TSA screening with it. Six lanes were instantly closed as a result of the fake IED, resulting in hundreds of additional travelers being inconvenienced.
While the tourist who carried the item was detained, the agents already had their training, which was a blessing in disguise.