My worst neighbors ever were in college. They invited my friend and I to a party and I decided to leave early because I need my sleep and we had an early class the next day. My friend wanted to stay so I gave her my key and went to bed. And the next morning she was still gone, downstairs, sleeping. They had slipped her a pill and raped her. Obviously it was an aweful experience and I still feel responsible because I left her there alone. Worst neighbors ever, and I had to see them for a whole year after that.
Another not so bad, but still sucky neighbor was when we lived in a townhouse. She never had her dogs on a leash and they'd wander and poo in everyones yard. One day dh was walking our dog and I heard dh screaming at someone. Apparently her dog, not on a leash, came charging at my dog ready to attack. Dh stuck his foot out to stop him. He felt awful about it, but what do you do when your dog is about to be attacked??? He called the police but nothing happened. Luckily she was a renter and left soon after.