Help? Neighbor is threatening legal action/lawsuit for a stupid prank.

I have a neighbor with a BMW which he spends hours every week lovingly cleaning while blasting shitty music. He also did something with the exhaust pipe of the car, where it rumbles really loud at all hours of the night when he revs up the engine. I've asked him to keep it down at night, which he did for a couple of days, after which he was back at it. I asked him again, and then he just ignored completely.

So I devised a plan. This guy is very sensitive with the age of his car, and put a sticker over the dates on the car's license plates. It's not even that old, from 2017, but apparently he likes people to think he's driving a brand new car.

Every night he revved the car up, I would jab him where it hurts. While he was fast asleep in the morning, and when on my way to work, I would take the stickers off, exposing the age of the car. He would first replace the stickers. Then he started using a water-based paint, which I found a wet paper towel would easily clean up. Finally he started using enamel paint, but a quick rub of a cotton ball with my daughter's nail polish remover would do the trick. All in all, I did this about a dozen times starting in mid December.

After a night of revving again last night, I'm back to wiping his plates before getting in my car. I start, his car jiggles and he sits up in the back seat catching me as I'm up by the front end. What started with obscenities, almost came to blows, and finally ended with him swearing to sue me for damaging personal property.

I didn't damage anything. I've been at the office today wondering how far he could take this. If I'm not mistaken, the registration plates, are not even his personal property, but the government's, and if anything, would a law suit incriminate his own actions of modification of gov't property? If he brings the police into this, what would they do?

If you can point me to any legislation about defacing or obstruction of government property, I could use this to claim, that if anything, I was actually righting his wrong?