I looked and looked for the origin of this expression, but with no luck. It must just be due to the cat's obvious superiority in all things.
[ADDED: Yay! Sissy found it:
The cat's pajamas (and the cat's meow, the cat's whiskers), was a very popular expression in the 1920s, associated with the daring and unconventional jazz-age flappers. H.L. Mencken describes the flapper as a young woman who "has forgotten how to simper; she seldom blushes; and it is impossible to shock her." The lexicographers William and Mary Morris suggest that these "cat" expressions may have originated even earlier, first used in girls' schools. Cat's pajamas ]
From HowStuffWorks*, we learn that:
Whiskers help the cat feel his way around. Whiskers are so sensitive that they can detect the slightest directional change in a breeze . . .
. . . a cat's whiskers are also a good indicator of his mood. When a cat is angry or feels defensive, the whiskers will be pulled back. Otherwise, when the cat is happy, curious or content, the whiskers will be more relaxed and pushed forward.
But the whisker's primary use is to help a cat judge whether or not he'll fit through an opening.
And we all know that cats greatly enjoy fitting through openings, especially those we want them to not fit through, like kitchen cabinet doors.
Here are some places we can all go this weekend:
* Note that HowStuffWorks, which one expects to be very 21st century, is still stuck in the singular- male- gender 80's. Apparently all cats, for example, are male. I thought that maybe they just trade off, but no. A quick perusal of the site demonstrates that these geeks think boys is all there is (unless, of course, the subject is specifically female.) One would think they would know more about how things work.