There's no prize for being the second most grumpy cat on the Internet, but frankly, there damn well should be. Anyway, Pokey is Grumpy's brother and he's not particularly happy about it...
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In this picture, Pokey is grumpy because he has realized that he will never be quite as grumpy as his brother, Grumpy Cat. In other words, Pokey is being meta-grumpy, which is impressive, and difficult to pull off while also frowning significantly.