Dodgiest carry-on item I recall dealing with was a practice hand grenade (looks exactly like a real one to the uninitiated, but has no explosive) in the luggage of a fourteen year old U/M. A teenage friend had mailed it to him from the USA as a ‘souvenir’ 
so it had made it through the postal screening process. It had already travelled with him as carry on from a regional port (pre 9/11 screening) and was only picked up in transit at a major airport. Scared the 
out of the X-ray operator.
I also remember a similarly aged kid with a telescopic baton in his carry-on, he was travelling with his Dad who was most indignant about his son's bag being searched until the item was produced, at which stage he became MOST apologetic...claimed (plausibly) that he had no idea his son had such a thing.
Coming soon to an 18th birthday party near you
Who the adults who sent them on their way.
Scary people. I'm sure we all agree.