sankyo & nikkyo hurt you know.
Seriously though, if the dude is disruptive, as a teacher make it clear you wont tolerate this behavior.
(No Im not talking about resorting to violence... the opening was a joke.)
They own the dojo, true, but they asked YOU to teach.
Can it be that they want this guy to teach now?
If so, then that is not a problem either, as you go with the flow of things.
Why resist, and make things worse, if that is the case?
Perhaps you two can try to learn from each other...maybe with a little humility see why he does his techniques how he does it.
You never know, you might just have a new assistant teacher. (though I agree that many would say it would be nice to evolve the attitude a bit.)