If I had an arch enemy (which people should be glad I dont) I would go for some old fashioned anarchist cookbook-esque mayhem.
Spread some sodium chloride on his lawn in phallic shapes and "Fuck you"s
Take a lightbulb from the kitchen and fill it up with some gunpowder and screw it back in
Fill all the locks in his house with rubber cement
Mutilate his couch cushions, then flip them over
And some other stuff I would get creative with
Okay okay. I'd leave some time on his microwave. Change location of everything in his house according to fengshui then set all the clocks in his place to go off at fifteen minute intervals ( they would all be hidden ) I would replace all the salt in his house with sugar and vice versa. Put some dark chocolate powder in the coffee grounds. Replace every song on either cd, mp3 player, or television with nickelback but keep the titles to the previous songs. Then I'd pay some punk kid to blast green day from his car in front of his place in the dead of night.