I had a "friend" in college who let me move into his house (he had a 3 bedroom house to himself) after me and an ex split up and I wanted out of the apartment we'd shared.

Things were ok at first, but he got more and more crazy. His mom would come to visit and her sheep dog would take a massive shit in my room every single time, and they'd act oblivious to it and refuse to clean it up. He didn't take care of his dogs at all, and they'd shit and piss all over the house, and it was just disgusting.

On top of that, he had a really sweet girlfriend, who he was constantly cheating on with huge fat chicks. He was this skinny little red head kid and he'd bring home these 300lb girls and they'd fuck loudly in his bedroom.

I finally just couldn't take it anymore and moved out. When I moved out, I'd already paid the next months rent. I asked for it back. He said he'd already spent it, so I couldn't get it back. Then, he called the police and told them I was a squatter, he'd came home from class to find me in his house and had no idea who I was.

The cops knew him, his dad had been the city garbage manager and had been brutally murdered a few years before, so they felt bad. Even though I had proof I'd been living there for months, including carbon copies of rent checks he'd cashed, they told me I had to be out immediately. Luckily, I had somewhere else to go.

I never did do any revenge. I'd always wanted to get some cadaverine, which is what they use to train dogs that find corpses. You can order it online from medical supply companies. Then use a syringe and squirt it through the door seal into his vehicles. From what I've read, you'll never get the smell out and your vehicles will reek like death.