I don't know who the mofo is...

but I'm inclined to blame the library.

I get an email from the library notifying me of several overdue accounts. However, I haven't checked anything out in a couple of months from this particular library, so I check my account online and, to my surprise, discover three test prep books on my account. Um...considering that I'm out of school and working as a school librarian with a recently acquired MLIS, I don't have any immediate plans to return to school.
When I call the library, the librarian informs me that I must have checked out the books after requesting them since I still have my physical library card in my possession. I insist that I never checked those books out and she just tells me to call the downtown branch, which I do. 
The librarian there basically expires my card so I need to pay a replacement fee for a new one and present an ID whenever I check anything else out and, oh, I need to be especially careful because I've used up all three of my claims for disputed items.

I'd like to blame whoever used my "card" to request and check out the items, but I'm really not sure how this could have happened, which is why I'm more inclined to assume that the library is at fault. 

Maybe some of the public library folks on here could give some input on how this could have happened.