Hmm... I don't know. Sure, the rock is decent sized, but heavy. Unless Vince is strong enough to throw the rock with lightning speed, the maniac could still see the throw coming a mile away, and dodge it. It's usually the speed of the weapon which it is thrown, rather that it's weight, that could result in a KO. If you're thinking of physics here...
So, my option would be D. Switch weapons, though I doubt there's any time now.