A Foul Family
We lived in what looked like a mansion-type house that was rented out to three different families. My family lived on the bottom floor, and a family of six lived above us. Every morning they would stomp around the house and make as much noise as possible to wake each other up for school.
Since we were on the bottom floor, we had free reign of the backyard, whereas the other two families barely bothered to use it. They would frequently dump garbage and other random stuff off of the balcony into the yard and never bother cleaning it up.
We would have to tend to it daily since we had two dogs and an outdoor cat. The landlord eventually kicked them out, and when he went to inspect their apartment, he made a disturbing discovery. Their apartment was full of soda bottles, as well as mold growing in multiple rooms. Story credit: Reddit