I own a book ("The never ending story") that a friend of mine vomited on fifteen years ago. About half of the pages are still stained.
My copy of Ken Grimwood's "Replay" looks like someone's skewered it. There's a hole that goes straight through the whole paperback. Not sure how that happened, but it doesn't obscure any words, so it's just kind of charming, really. My copy of "Blindness" is held together by large amounts of duct tape.
I /really/ like creased backs on paperbacks. It makes them look cosy, dangit!
So, book-lovers, beware my home; a visit may scar you for life.
I'm quite kind towards them all though, despite these extreme examples, and I never intentionally do them harm. But yes, once I'm done with a paperback, its back tends to look like it's been through pregnancy.
I did, however, cringe when I saw how a friend of mine handled a hardcover book she'd just bought. Some of you may wish to avert your eyes, as it's not a story for those of a delicate disposition.
The first thing she did was open it to somewhere near the middle, and make the front and back cover lie flat against a tabletop, while she pulled her fist along the crevice betwixt the two halves. I could swear I heard a feeble moan just before its strained back snapped.
Why'd she do it? Because she likes to keep books lying flat on the table while reading, without having to hold the pages open.