This is unlocked when you get stuck in the elevator in the library, because you have to much stuff in your inventory.
Read elsewhere that you need to fill the first page of your inventory (15 items) for this to happen, but neither that nor 16 items wasn't enough for me.
I managed to unlock this on my first visit to the library during the playthrough where I spent money, and I had the following 18 items in my inventory:
- Box of pens
- Copy paper
- Library access card
- The 8 books from the shelves between the supply room and the photocopier in
the library (these count as 8 separate items)
- Discount flyer for the copy shop
- Lottery ticket
- ID photos
- Bottle with pig's blood