How do i get back at a boss?

My boss has just written me a bad reference as he wants me to stay, my other refs were very good so i may still get the job and he has just given me a passing shot so to speak. All i want to do is smash his face with a cricket bat as we see each other outside work quite alot socialy and i regarded him as a friend. Any ideas execpt violence as he is the type to go to the law? he is on holiday untill next monday so i have so time to plan but i am blinded by rage, help!