Kirby looked cross in the US... he used to be such a good boy
Over the years, Kirby has picked up a bit of a reputation for developing an angry expression on the front cover of his games in the US--a very different look to the chipper Kirby in Japan. Kumazaki recently explained to GameSpot that the difference is down to regional marketing. "For the Japanese versions we are, at [Kirby series developer] HAL, involved in everything throughout development, including the package design. The most powerful image of Kirby is that cute image, we think that's the one that appeals to the widest audience." That explains the Japanese Kirby, then, but Kumazaki adds that Nintendo of America thinks a "tough" Kirby is more appealing to a Western audience. Now you know.
Hence the phrase "he's one tough cream puff"