This was suggested to me by the thread concerning cameras on airlines.
Some years ago, I was taking photos along a clifftop close to where I used to live, when I saw a person with a dog approaching. Knowing some dogs can feel threatened by what they perceive as sticks, I collapsed my monopod and held it beside me. The dog and owner passed me by, we exchanged 'Good mornings', and headed in our separate directions. Not long after, a Police Range Rover came bounding over the rough turf towards me, and I was ordered to lie on the ground by apparently armed officers.
I promptly did so, and the OIC (I think a sergeant) stood with his standard issue very close to my head, and demanded 'Where is it ?' I enquired what he was looking for, and he said 'Your gun !'
Apparently, the dog owner had seen me collapse the monopod, assumed it was a firearm of some kind, and called the police !
I was allowed to stand, still covered by firearms, and I explained the situation, showing them the monopod and opening my bag so they could see the contents. They even took each roll of 35mm film from its container to check the contents. Finding nothing, they then departed, leaving me to pick up my equipment and restore it to my bag. No word of apology.