As somebody who works in a library, I am glad that your passion for annotating books doesn’t apply to library books. You’d be surprised how many of our patrons write in our books — they underline, highlight, make marginal notations, and sometime take it upon themselves to correct errors (or cross out anything having to do with sex.) Doing this with your own copy of a book is fabulous (except the crossing-out-sex part — that’s just weird.) But doing it to a library book is not okay.