I think most of us had at least returned something, either via mail or by going back to the store... Question is, have you ever forgot to return something that came with the purchase? This could be anything that was small and simple, actually!

I know for sure I did once.

Back when I was getting Rock Band 3, I was looking for the original disc... Ended up buying the MadCatz disc from Amazon on accident (Which was something I didn't want to do). The MadCatz game came with a code to download 5 Red Hot Chilli Peppers songs... Well, I returned the MadCatz game back to the originally owner and got a full refund... But forgot to return the code back to him so kinda got 5 free songs for my game and yes, did used the code...