Stupid ex-library clerk tricks

So I go to the library last night, to return things. Go and check my account, come back to pick up the holds that are in, and one of the clerks hands me two empty CD cases, saying that I forgot to put the CDs back in. What do I do? I open both cases, and verify that they are, indeed, empty. Idiot. How many times did I roll my eyes at people who did that, when I was a library clerk myself? Idiot.