I believe that it's better to store glasses/cups right-side-up in the cupboard, but at work everyone stores them upside-down.  Which is safer/more sanitary? 
Where did this urban myth start? Storing a cup upside down has few real advantages. The usual story is that it prevents cockroaches from crawling all over the cups. If this is the problem, then why don't people store their plates and bowls upside down, which roaches etc would definitely crawl over.   I might be wrong, but, my experience is that roaches that fall into a cup, stay there. Evidenced by the poor woman who discovered an upturned roach in the bottom of her parfait glass under the trifle, at a wedding reception where I was working. The trifle was brilliant up to that point. I'll never forget the muffled squealing! Sorry. I do store glasses or mugs upside down, sometimes, if the base is small and the rim large, to avoid them toppling over. Storing cups, glasses, mugs upside down:  Pros   May save some airborne dust, but, in a cupboard and used regularly, dust rarely has time to accumulate. I swill out my cups with left over boiling water (in the case of tea) anyway. Would stop roaches etc from entering the cup but, negated by the fact that the rim is definitely exposed to a dirty surface.  Prevents cups toppling if base is significantly smaller than the rim. Incidentally, if none of this matters to you, cups/mugs stored alternatively, in both orientations, may allow for more efficient storage. This allows people the option of both preferences.   Cons   Rim of cup exposed to dirty, unhygienic dirt and cockroach surface, rarely cleaned. Traps remnant moisture possibly allowing the dirty cupboard surface particles to stick to the rim of the cup much like the salt on a margarita glass.  