Richard de Bury was an English cleric who lived in the 14th century and wrote in Latin a book called Philobiblon; the love of books. In one segment, he describes the carelessness with which some students treat books:
"You may happen to see some headstrong youth lazily lounging over his studies ... He does not fear to eat fruit or cheese over an open book, or carelessly to carry a cup to and from his mouth ... Aye, and then hastily folding his arms he leans forward on the book, and by a brief spell of study invites a prolonged nap; and then, by way of mending the wrinkles, he folds back the margin of the leaves, to no small injury of the book.
Now the rain is over and gone, and the flowers have appeared in our land. Then the scholar we are speaking of, a neglecter rather than an inspector of books, will stuff his volume with violets, and primroses, with roses and quatrefoil. Then he will use his wet and perspiring hands to turn over the volumes; then he will thump the white vellum with gloves covered with all kinds of dust, and with his finger clad in long-used leather will hunt line by line through the page; then at the sting of the biting flea the sacred book is flung aside, and is hardly shut for another month, until it is so full of dust that has found its way within, that it resists the effort to close it."
The above paragraphs are a generously abbreviated version of de Bury's rant on misuse of books. It's an amusingly artistic treatment of the subject, and I can imagine a library putting up some of these sentences as illustrated posters.