New Super Mario Bros Wii, World 8, the lava levels. After getting my ass kicked for the xxxth time I said fuck it. The fact that you have to repeat levels you already have beaten when you die, plus the klunky ass controls of Mario made me run out of patience. Call me a noob if you want, but that was it.
On the other hand, I beat DKCR with all the optional temples, which is much more difficult than Mario, but the controls were tight and it didn't make me repeat the shit I've already done when I died.
Generally I hate being punished with repeating stuff when I fail, especially when the game isn't very fun at all. The same happened with Demon Souls.