I don’t have enough room in my cupboard to have one cup to a stack. So I stack them all together, usually leave them upright because that’s how I hold them. But it doesn’t bother me either way. My roomie leaves hers upside down and I respect that when I use one of hers, wash it, and put it away.
I much prefer plastic to glass anyway. Stacks better with no risk of breakage. As long as they’re properly dried out before going in the cabinet, stacking is fine.
Willy-nilly, mostly up, sometimes down. I mostly just don’t think about it.
It depends on the glass.
Tumblers and some mugs- upside side down
goblets, wineglasses, other mugs - right side up
The mugs depend on where they are stored.
I didn’t vote since there isn’t an option for both.
Is there a name for the mental condition that’s the opposite of OCD? 
healthy indifference.
Leave-well-enough-alone order?
Don’t-fix-what-ain’t-broke syndrome?
(Don’t worry, I’m a chronic sufferer, as well.)
Dry them on the dish drainer upside down, store them right side up. Never questioned it, never had an issue with it.
My husband is the opposite. He’s another OCD-er when it comes to dishware. I blame it on the crappy apartments he lived in after college.
If people put their glasses standing up then dirt and other stuff can get into the cups. Would you rather just wipe the rim off the glass or have to re-wash the whole thing???
Down, lest you find a dead bug, or a live one, floating in your early-morning coffee.
Depends.
Cabinet with glass doors: right-side-up. Cabinet without glass doors: cups go right-side-up (stability, at least with both Mom’s and Grandma’s models), glasses and mugs go upside-down. Mugs tree: ehr, kind of diagonal.
Or, just don’t worry about the “dirt and other stuff.” I’ve never given it a thought.
But diagonal up or diagonal down?