If the glasses are at all damp, it may make sense to store them up-side-down.
In bars and restaurants, you often see plastic mesh like this: That webbing lines trays, shelves and the area beside the sink for drying dishes.
The mesh keeps the dishes or glasses, which may still be damp, from actually touching the surface they're sitting on.
In the case of glasses, it also keeps the glasses from forming a seal to the surface beneath.
That mesh often gets cleaned, as does the surface under them.
In that case, it makes sense to store glasses up-side-down.
Do you have mesh lining your cabinet?
Are the cabinet shelves wiped down regularly?
If not, it is far more sanitary to store your glasses right-side-up, and to be sure that they are dry before they are put away.
cooking.stackexchange.com/users/20183/Jolenealaska
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.
cooking.stackexchange.com/users/35469/Michael Cussen
Bars and restaurants store glasses upside down to keep them clean from splashes of drink/food
while in racks in the busy production areas.
There is little chance of trapped moisture causing mould etc.
as most glasses are used every day.
It is more awkward to turn glasses over as they are served, but saves having to cover them all the time This is generally not a problem in a domestic environment, and glasses should be stored in normal position to ensure they do not retain any trapped moisture and therefore grow mould etc.
cooking.stackexchange.com/users/3203/TFD
Some people don't want to put the part of the glass your mouth touches on the possibly dirty cupboard bottom.
Let's assume that the insides of your cupboards are clean enough (you have no mice, rodents etc) that this is not an issue.
Further, let's assume that you have cupboard doors and the aforementioned lack of vermin, so worrying about dust and pests getting into an upturned glass is not an issue.
What does that leave you, if cleanliness is not a problem?
I stack many (but not all) of my cups and glasses.
Grabbing the top one from an upside-down stack is easy - you have the whole cup surface to grab.
Grabbing the top one from a right-side up stack is hard - you have to grab just the little bit that sticks out the top.
Therefore all stackable cups go in upside down.
For the sake of consistency, so do the others.
cooking.stackexchange.com/users/304/Kate Gregory
If you ever spent time in a hospital setting, you would have been instructed to place cups/glassware right-side up in cupboards to prevent contamination from germs.
It makes sense.
You put your lips against the rim, but never ever lick the bottom of a cup or glass.
cooking.stackexchange.com/users/47473/Jack
rim side down.
i was raised in a household where my parents were depression era kids.
they got in the habit of putting glassware rim side down to avoid the glasses filling with dust from the dustbowl clouds that blew through on a regular basis.
it just stuck over the generations and became how you do things in our house.
cooking.stackexchange.com/users/52061/jerry
I get the stated question is more sanitary Consider what is easier.
A lot of people do what is easy.
They come out of the dishwasher up side down.
I worked a dishwasher in a restaurant and I could pull 4 out of the rack at a time and put them on the shelf.
If I had to grab them one at a time and flip them it would take 4 times as long.
If you are stacking them and bringing them out in a stack the stack is more stable.
Can pull them off the stack more easily up side down.
If they bind and have to wiggle it is easier up side down.
cooking.stackexchange.com/users/45636/paparazzo
Logically, I would choose to store them upside-down, both to 1) Maintain a cleaner/more sterile glass interior, and 2) having slightly hard water, to avoid a cloudy spot drying in the bottom of the glass (if they are stored before being fully dry).
That being said, I still tend to store them right side-up for aesthetic reasons.
cooking.stackexchange.com/users/31324/Chris R
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?
How should glasses/cups be oriented in storage?
cooking.stackexchange.com
<food-safety><utensils>
cooking.stackexchange.com/questions/52045
cooking.stackexchange.com/users/31291/Pat
Storing upside down may prevent accumulation of airborne dust and unsightly spots if the glasses are not completely dry, as well as to prevent some glasses from toppling over. However, the risk of contamination from dust in a cupboard is low, whereas storing upside down exposes the lip to cupboard surfaces that may be contaminated. Many people believe storing glasses rim side down is the more hygienic option as it stops bugs crawling inside and moisture and dust collecting in the bottom. On the other hand, people say that the rim may be contaminated from contact with the surface and so right way up is the more hygienic option.
Glasses are stored upside down to prevent insects from climbing inside, to stop dust and stop any moisture collecting in the bottom. Storing glasses the right way up stops the rim from getting dirty if the surface is not clean.