The thing to remember is to stay just the right side of the law so that if you do get caught, you won't get prosecuted. But try not to get caught (obviously).
If you really want to be Machiavellian-Evil, and actually fuck him up in a serious way, you could wait until he's out of the office and take his credit card from his wallet and note down the details (I often found bosses would wander out of the office, leaving their jacket and wallets on the back of their chair). Then simply sign him up to as many kiidie porn sites as you can and wait for Operation Trident to net him.
Alternatively, you could scratch irritating phrases into his car with your keys, or give out his email, home address and telephone number to spam/junk mail/porn senders.
Or you could do what I once did to someone, and enlist them in the army (Territorials might be easier to achieve).
Personally, I think that the need for revenge only goes to show how much this person against whom you feel agrieved is still affecting your life, and is effectively still controling you. However, since I know you're both a bitter Irishman, and a bear (not noted for their diplomacy), I doubt you'll listen to my sage-like wisdom.
