Sick apartment-mates who are not careful about their germs.
In all fairness, I think I might be the tiniest bit germophobic, so perhaps it's just me...but I really think it's polite to keep one's germs confined to one's own room, instead of lying on the couch in the living room/dining room for days on end, spewing forth a veritable virus army that would only be too happy to make my life miserable. This is the busiest time of the year and I can't afford to get sick.
Fea--What you call naive and idealistic, I call optimistic. There aren't enough of us in the world these days. I'm darn proud of those characteristics in myself, and you should be too. There's no rule that says that once you hit a certain age, you must stop believing in everything worthwhile.