At the base of a bullet there is a small round circle, called the primer (See Diagram) Normally in a gun the firing pin hits the primer in the middle, which in turn ignites the the gunpowder and sends the bullet traveling from the barrel.
If you were to drop (more like throw) the bullet in a way that some sharp concentrated object hit the primer just right, it could discharge. But it’s not easy to do, think something more along the lines of using a nail and hammer on it and still having a hard time.
And if it did discharge, it wouldn’t be that dangerous. More like a firecracker since the explosion isn’t compressed (gun barrel), and there is nothing (gun barrel) channeling the bullet with the (highly compressed) explosion behind it. All of the force would expand outwards 360°, dissipating extremely fast in an exponential fashion.
There’d be a pop, a quick flash, and the bullet would plop over on the ground somewhere. It’s certainly not like movies.