SNES: Primal Rage (What the frack was I thinking? The arcade version isn't much better...either.), Super Gameboy adapter (just played a ton of Kirby's Dream Land on the SNES, and plus used it as a party demo thingy), Shaq Fu (yeah, the ultra cheap price was a dead giveaway, even if it was practically brand new)
Gameboy: Mortal Kombat (I bought that multicart especially for MKI - terrible quality of game, and terrible sound effects - only cool thing was playing as Goro)
Launch day original DS - I had one dead pixel, and it sat on the shelf for ages. Also, I got more out of the Metroid First Hunt demo than anything else. Finally sold it a couple of months later, only to rebuy it for Pokemon.
Tamagotchi for the PC. Terrible interface, terrible gameplay and really why? (It was at a Surplus Shop in my hometown.)
Tropico 1 - the disk was scratched. It was at Wal-mart, and their return policy was really dismaying.
Monster Hunter Tri 3G - Japanese version. I thought I could turn a profit on ebay, but apparently nope....people rather buy games from sellers who regularly sell them.