Re: how many back talk would you take?
Like Basia said, "back talk" isn't really a phrase I associate with adult conversation.
But if he refuses to accept instruction, the best answer is to just ignore him and get on with your life. That's especially true if you're not actually teaching the class.
If you *are* teaching, then you have a responsibility to make sure that he doesn't injure anyone, disrupt the class, or undermine what you're trying to teach. Throwing him until he can't stand up seems to be the classical solution. (Or should I say, showing that what you're doing is effective, repeatedly, until he either agrees with you or is too tired to argue.)