A free weeks lessons sounds like another great idea.
Yhis thread was not started for me to take credit foir anything on my part. I wish those reading it for the first time or 2nd or whatever would continue to express themsleves on how to deal with people who come into a school and issue a challange.
I believe the point (made several times in the course of the thread) that this is a teen could be drawn out a little further.
Just as a counterpoint, an adult who would do something like this, in my mind, is on his own. Several ways have been suggested to get rid of such a person. My personal favorite was in another thread, where someone mentioned their sifu responded to a challenge of 'What if I hit you', with 'Come up and try it'. The challenger did for about five minutes, left and never came back. That's a different,
much smaller liability issue to me, so more easily handled (Hey, if an adult comes into my class and tries to attack me, and all I do is block, what ammunition does he have to tell the authorities).
But a teen, well, I work with challenging teens (by choice

), and often the old maxim is true:
Obnoxious behavior is a cry for help. So as much as we hate it, sometimes being able to see past the surface behavior to the kid's real need is what might really turn that adolescent around--or just continue what he may have started, and not know how to finish (the passage from teenager to adulthood).
So,
ts, I know you want to get the spotlight off your self and onto solutions, but still gotta say again, kudos for your handling of this so far. And as far as how to go forward, I'd just say that your willingness and effort to pull this kid into the fold of your training family (one week free lessons, or whatever) is the approach I would lean toward.