There are a few I can think of, but none more annoying then the final levels of the Ninja Gaiden remake. The game had done a pretty good job of being hard without being cheap, but after you beat Alma's second form it seems to stop giving two shits. Now all of the sudden the game's flooded with an infinite amount of tiny ghost fish that respawn instantly and can kill you in seconds, plus you're forced to fight three bosses in a row (two of which are resurected earlier bosses) with no save points in between. Getting through these levels is rewarding in the same way getting a root canal is rewarding.