Take a fire extinguisher. For starters, go to the girls dorm and do something that will turn the teacher's attention on you.
When they start running towards you you ought to run as well, right? Well, to show your really tough, here's a technique.
Spray the teacher with your fire extinguisher. When they wave their hands over their faces, attack them normally by punching and kicking them. Repeat this process until you manage to weaken them, as in deplete their health to zero.
When you are doing this process, whatever you do, don't press R! If you do, then you will drop the fire extinglisher and there is a high chance you will get busted.