In a shared living space, tidiness is usually a necessity for sanity. If an individual is really neat and clean with their own room and personal belongings, having a roommate who does not care about their stuff and leaves the shared area a mess can become a great annoyance. An apartment and shared space is considered a sanctuary away from the stresses of everyday life.
Noise can be a contributing factor toward the creation of a serene home environment. However, with a noisy housemate or an individual who shares the same bedroom, rest and quiet time is difficult. This can be annoying for an individual when the person is trying to study, watch a program or read. Roommates who make noise while their housemate is attempting to sleep is an annoying factor.
While sharing a house, apartment or room does mean that a variety of people come and go to visit your roommates, a roommate's guest who stays for an extended period of time or shows up when not invited constantly can be a source of annoyance to individuals. They no longer feel like the apartment is their space; it seems that they have another roommate, but one who is not paying rent.
While sharing a space is expected with a roommate, sharing food is not. Roommates must respect each other's boundaries, and to do so, you must be aware of them. A roommate who constantly takes your food is not only annoying, but is also expensive. Differing food routines also can cause problems; for instance, the dishes are not being cleaned so you must always wash them before you can eat, or you are both preparing food at the same time but the roommate hogs up the entire cooking space. Roommates must set up rules and boundaries -- and then respect them.