I've had several cases of hand-luggage being left aboard, and I'm amazed how "security" just blithely take it from the rack. In one case I was told that if I wanted the bomb-squad called, it would meant the evacuation of the finger. "Fine, do that". The next thing I knew was a young man came along and, after I'd got the crew well out of the vicinity of the aircraft, happily took the bag down and opened it!!! Luckily, it was nothing, but the fact that it contained three passports should have set alarms ringing.
I've also offloaded passengers who think it's funny to tell the cabin crew that there is a bomb in their hold luggage. Off, escorted by a couple of hefty policemen.