Here are the ones that I think are most common among society
1) Dirty dishes (I lived with people who delayed doing dishes...I even had one roommate who would let food rot and mold in her room on it's plate in it's bowl.)
2) A dirty house (Seriously...clean up after yourself...it doesn't have to be spotless but keep it together.)
3) Smoking, drinking, and drugs (enough said)
4) Not taking care of yourself (e.g. poor hygiene)
I could probably think of a few more...but I don't want to sound like a pessimist.