Dumbass at that point just don't even return the book

I fail to see how you see this as an "FML". You should have expected a huge fine when you returned the book!

You should've left, came back saying you lost it, and paid like 15 dollars for it.

haha ********

Being as I am broke I have found ways to get around such dilemmas. You should have returned the book to the shelf prior to checking it back in and speaking with the librarian. When they said that you owed $100 due to the book still being checked out you simply tell them you have not had that book for years and that it is probably on the shelf. After you "find" the book on the shelf then you can be on your way. This used to work very well at the video store, when they were still around.

You should´ve put it in the mailbox.

Library fines tend to accrue over time. If you had it for years, didn't you realize there would be a large fine?

By this time you should've just kept quiet and kept the book. I mean, years? They've already replaced it. YDI

Tried to do the right thing and she called the cops!?

And I thought owing a nickel for late books was a problem.