I agree yet again diffuse the situation and deal with the student when everything is calm.
As a parent, do you believe the same? As a parent, if you were facing a defiant child would you let it play out and try to address the situation at a different time? (I am always a little surprised at how I come across in internet forums, because my family and friends have been a bit aghast at how permissive I was with my kids, and how I never punished them. Other kids were grounded, put in time out, and I usually opted to just try to reason with them. So.)
Sometimes, you just have to fall back on "because I said so". We're going to get in the car and leave the pool because I said so. You're not spending your allowance on a bic lighter because I said so. You're taking that facebook post making fun of the teacher off your wall because I said so. These are all three things that come to the top of my head that "I said so" and I don't care if it causes a confrontation and "loss of face", I said so and that's the way it is.
So, in those situations, do you not see the value in drawing a line in the sand right now, no negotiations, I said so?