What's the worst "neighbour from hell" behaviour you've witnessed?

Source.

Get drunk, scream at the top of their lungs at each other in the middle of the night [in their backyard], slam house doors, and by 6am the guy woukd jump in his camo truck and rev the engine [which was LOUD as f.uck]. This happened at least once a week...

I had a neighbor that was always snooping around my yard. He kept on telling me how the old neighbors did it and then he would get upset if my kids were playing to close to his yard. What a ass

One time I was living in a two story house & a 3 person family moved in down stairs. The guy waited till I went to work & he hooked up his electric power through my power lines under the house. I didn't find out till I got a $1000 bill the next month, so I looked at the two different meters & noticed theirs wasn't moving but the a.c. unit was on; so I turned my breakers off & the a.c. unit quit to. Needless to say I called the power company & the police, the guy admitted to stealing my power & went to jail. The power company reduced my bill back to the month before & charged him the rest.

My own behavior lol haha

There was the time i put a built 350 in my camaro and fired it up open headers at 3 in the morning outside my neighboors bedroom and then did a bunch of burnies

you and I would have been fighting lol

I would have to say when my down stairs neighbors would have their music so loud it was like i had it on full blast in my apt, you could hear every word perfectly clear. It happened all the time at like 4am when they was getting ready for work & i was getting home from work trying to fall asleep