I don't care if I make my things dirty. Especially with my personal dirt. I don't allow myself to make other people's things dirty or for other people to dirty my things, though.
Also, if you wear glasses for 27 years, you eventually get used to the idea that no matter how much grease and film and dust you get on your glass surface, it'll wipe off.
I wouldn't with a tablet or whatever for obvious reasons, using a keyboard or a mouse with non dirty hands is next to impossible though (and if you manage to do that you're probably a neurotic fuckstick); oftentimes the mouse/keyboard becomes more dirty than anything you could possibly eat. You rest your hand on your mouse for hours sometimes, of course its going to be dirty.
Not really. I mean, sometimes I would try to use the least covered finger to tap the left mouse button to start a movie or play the next episode of a TV show I was watching. I would never just full on grab something like that if my hands were covered in food residue. I would lick them clean with my tongue or wipe them on my pants or some kind of wash cloth and then grab the thing.