do it quickly, decisively and cleanly, and then stop.

I once punched a dude that was fucking with me in the mouth right in the middle of science class while the teacher had her back to us. He just sat there with a stunned look on his face and stopped. Later after school I ran into him coming from the other direction while I was leaving and he was yelling threatening shit while we were approaching each other. I just kept quiet and kept walking towards him and when I got within speaking distance he said something like "you like punching people in the mouth?" and I was just like "yeah" and kept walking past him. I really thought he was going to attack me but he didn't do anything and didn't fuck with me after that.