Gunbrella
I was visiting my mother recently and it was raining so I borrowed an umbrella. Maybe I should add that I was going out so borrowed an umbrella since it wasn't raining inside the house and anyway opening umbrellas inside is unlucky. That's why in the film clip below my brother is opening the umbrella just outside the back door. Anyway the thing is that when I pressed the button to open the umbrella it exploded out of my hand, the spring was far too strong. I actually think it could do some damage and was certain that this wasn't an umbrella at all but some sort of anti mugging device disguised as an umbrella. Once you knew what was going to happen it wasn't quite so shocking but it still has quite a kick. It's all to do with Newton's 3rd law of course, as the umbrella end is forced forwards the handle experiences an equal and opposite force pushing it into your hand.