I won't fold corners of a book if it's from a library or borrowed from somewhere else, but if it's my book I'll be writing in the margins, underlining shit and folding corners to my heart's content.

When I buy a second-hand book and see someone else has done that it gives me a warm feeling because I know someone else loved that book.

In German, they translate to Donkey-ears.

Ah I never knew that! It's the same in Dutch too: ezelsoren.