I find it utterly repulsive when people lick their fingers before touching paper or when turning the page of a book. It's so, so unsanitary and unnecessary and I can't help but think someone a savage of some kind when I see them do it.
This one of my biggest "minor" peeves. And so many librarians do it!! I remember sitting in my primary school library as a young child watching the librarian demonstrate to us How To Turn Pages Properly and feeling sick when she said we need to do that. Just watching her was enough to gross me out, since my mother had a very large library of books I loved looking through and I'd always been taught how to gently rub near the corner of the page to be able to turn it without damage (if that makes sense? I have no trouble showing people including babies IRL but it's hard to describe).
I actually refused to use that unhygienic method, and I can recall several "discussions" where different librarians and teachers tried to correct me. Thankfully I was precociously eloquent in addition to being stubborn, and could talk my way around to being allowed to demonstrate MY way. My confidence combined with my obstinate insistance to "ask my mum if you don't believe me, she doesn't let me lick my finger to turn pages, that's yuck and spreads germs". Whilst I was right, and they certainly opened the door to that kind of response, I was lucky to get away with it. Basically telling a bunch of adults they're doing something disgusting and speading germs doesn't tend to go well for children unfortunately, no matter how right they may be.
The end result was that I was allowed to turn the pages my way, and I'd be responsible for any damage caused as a result (never happened, nor did they think it would, that was said for my classmates who were listening). Any other child who was inclined to turn pages without saliva (ya know, like most people manage to accomplish most opening/closing/turning things tasks that don't involve their mouths..) were allowed to, too, with the same "you break it, you bought it" clause.
I also learned VERY quickly to start using the top corners to turn pages to try and minimise my exposure to all that saliva. No way was I giving up books, but I wasn't going to *willingly* touch other people's spit, either!