1. Smoking. Maybe not such a problem in a brand-new dwelling with well isolated HVAC but it is a serious problem in older construction with poorly isolated HVAC. The negative effects vary from one room being smoky sometimes (usually a bathroom) to the entire place being unlivable at certain times of day.
2. Loud noises late at night. This can be parties, heavy footfalls, old pipes that clang or ring, animals, etc.
3. Pets. Besides the noise, the animals can be aggressive and their owners may not clean up their waste.
4. Water damage. If you can't tear the place down to the studs and rafters, you can't get rid of mold.
You can try to ask people to change, you can try to get the landlord involved, you can even get the cops involved. But it's a lot of hassle, it rarely fixes the problem long-term, and you will be seen as "that guy" who causes trouble.