Conker's Bad Fur Day.

First off, Rare had a reputation for good games, but they were cute, child friendly games. Conker was even a cute character with child friendly games. Then they made this... thing, which starts with Conker hungover from a night drinking and quickly descends into him fighting a giant poo monster. The game was rated R/18, which was crazy for Nintendo. The amount of little movie references everywhere was insane, also.

Those little French squirrels...