Trouble is this teenage school kid has never been given a smack in all the 12 years of his schooling. He's thus certain he can do anything he likes without any more consequences than possibly a detention in another few days' time from which he will probably go home early or kick a football around the school yard for 20 minutes, and then go home. No real punishment ever.
A swift and timely cuff in response to the egg should introduce him to the world called "reality". This may well be his first lesson in "take the reponsibility for your own actions". If you meet out a whack, expect one back immediately. The closer the punishment is to the offence, the more effective. No good waiting for the police to give him a tickle with a piece of wet lettuce, months down the track. Even more excuse for him to miss more school. Quick and efficient punishment is best and get on with it son, back to school.
