"Kind sir
I feel the need to respond to your attempt to dicipline me.
Surely you can see the outrageous penalty you havee assessed is too high a price.
Surely you can see the need to cool off and rethink things
Most likely you will realize you have over reacted and change your ruling.
Your students are watching you and will learn from your behaviour as much as mine.
All parties involved wish to end this in a mutually beneficial way.
So, in closing I hope to hear from you to establish a point of reconciliation.
Sincerely, Drew