This is simular to an example given by Massad Ayoob:
If a BG tries to take your gun out of your holster; he is doing it for one reason and that is to kill you; so deadly force is warrented by you.
If a BG comes at me with a taz or spray; he wants to immobilize me so he can do great bodily harm to me or kill me; I would use deadly force to stop him.
Just be careful its not some darn fool acting like an idiot with no intent to actually do you harm; however; that darn fool just put himself in serious harms way by acting the clown; I would treat the darn fool just as if he pointed a firearm at me.
"SOMETHING WICKED THIS WAY COMES"