Ideas from the internet.
1. Allow your own home to fall into disrepair, thereby lowering your neighbor's property value.
2. Dig a tunnel underneath your neighbor's house, and expand it until the hole is the size of the home's foundation; then, watch with glee as your neighbor's house collapses into the hole. Get out of the hole first though.
3. Call and have pizzas delivered to your neighbor's home. When he refuses to pay, tell the pizza man, "I'll take em, put em on my card." Then give him your neighbor's credit card number, which you stole somehow.
4. Pee on your lawn so it trickles into your neighbor's lawn. No one can stop you.
5. Ask your neighbor who he voted for. Then say, "I voted for the other guy." When he gets angry at your political preference, tell him, "Just kidding, I voted for the same guy you did. But now you insulted me so I'm voting for the other guy next time." His guilt will eat him alive.
6. Hire Megadeth to perform in your backyard late at night. Don't invite your neighbor (a big fan).
7. Does your neighbor have pets? Not any more, if you know what we mean.
8. Your neighbor comes home one day to find all of his furniture on his front lawn, painstakingly arranged in the exact same way it had been inside his house. While he's looking at that you hit him with a water balloon.
9. If you see your neighbor's wife having sex with a dog, get it on tape.
10. When your neighbor tells you he's going to Home Depot to get new batteries for his smoke alarms, reassure him, "No need. I made sure all your smoke alarms were working properly, just yesterday." As he thanks you, an almost imperceptible smile plays across your lips.