I bought a joystick for my MacIntosh (which would actually be my dumbest thing, but fortunately the computer was paid for by my father, not me, so I can't count that). I got it at EB, and traded in a bunch of games for it, including a lot of NES games that I received only a dollar or two a piece for. Most of these NES games were crap, but a few (Zelda 1 and 2, Metal Gear) I'll never forgive myself for trading in. Anyway, I get this joystick, and a few weeks later the computer stops working properly. Then, a few weeks after that, the joystick gets stepped on and broken. End result - I traded in most of my NES games and around $30 for a joystick I used for a few days.
Oh yeah, I also bought Star Wars Obi Wan for $50 when it first came out. Luckily, EB still had their open return policy, so I was rescued there.