Sometimes characters simply get forced to drop items they are holding because they get hit. I don't think it's something you can control that easilly (I could be wrong and I hope I am). My Toon has been forced to drop his bombs before, but I think that the bomb behaves as if it wasn't 'active' when it's dropped. Sort of like if you Z-drop a Bomb on the ground and then push it off a ledge, well when it's in the air falling, like that. This means that if it comes into contact with an opponent, it won't explode, but, it can be exploded if attacked (it also won't explode when it lands on the ground, rather it will bounce and then lay still on the ground until the timer explodes it).
Toon seems to drop the Bomb more frequently (from my personal observations) if he gets hit instantly after pulling out the bomb. But I think it can also work if he gets hit while in the animation of throwing the Bomb before he throws it.
So back to the example of Diddy randomly dropping the nana while in the tornado. I can only guess that he was interupted trying to do something like throw the nana or Z-drop it (even though I'm sure he was just mashing to get out) and that forced him to drop the nana. In theory, it should also work for Toon. As for getting it to happen on a regular basis, well that's something else and I can't test stuff right now.
