I've lived in an apartment for pretty much my whole life & have had my share of bad neighbours. I live on the top floor, so we don't have to worry too much about people stomping around above, but the people below can be just as much trouble! We've also gone through a few different owners of the building, some cared about who they let in, most didn't. One time the apartment below my bedroom turned into a flop house; they played very loud music at every hour, we began to get bugs migrating into our place (we had never had a pest problem previously), & these bastards wouldn't let the owner even look in their place to see what they have damaged. I have no idea how the legal system works for trying to evict someone, but it must have been pretty crummy because these creeps were in the building for quite a while. This was when I was much younger & still going to primary school. I moved into my Mum's room (her bedroom was above a different apartment), & she moved into the living room (we had a bed-couch). Once the land-lord got these people out & got the place fumigated, we never had a bug problem again.
Another time there was this creep who, once again, had the apartment below my room. He was a drug addict (fairly sure that he wasn't just a recreational user, but really addicted). He used to vacuum at all hours, mostly at 2am; regardless of all that vacuuming, his place was a pig sty! I felt sorry for his cat; this poor creature would come up to visit us for some attention, but then one day he just ran away & never came back. The dude was also always telling my Mum about how he was going to have his foot amputated; he did have something wrong with his foot, but in the time he lived here, he never had it cut off. Also this guy would every once in a while go into rehab & one time he left his cat locked in the apartment when he did this (a different cat). Whenever the cable TV went on the fritz, he would always shoot up the stairs to ask us if our cable was out; we never really thought about this until one time our cable went fuzzy & stayed like that for a few days (this was during one of his rehab stints), so we called the cable company. The cable guy came out & discovered that the bastard downstairs had spliced into our cable line & had it running into his apartment!! I went mental! If he were home, I would have gone downstairs & beat him with my baseball bat (I don't think I'd ever been so angry). Anyway, I think that was pretty much the end of him in our building.
I do have a couple of other stories, but I've gone on long enough.