The Cat’s Pyjamas
I seem to be wondering about truly random stuff lately. Not all of it cat related either! Maybe I really am turning in to a batty cat lady :p One of these random wanderings was on the phrase ‘the cats pyjamas’, as in ‘wow that’s so cool, it’s the cats pyjamas’!
Where do these phrases come from?? I pondered for a bit and then decided just to Google it 
And this is what I found on Urban Dictionary
1.
Cats pyjamas
An adjective used by hipsters of the 1920’s to describe a person who is the best at what they do.
Also used to describe another person who is genial and fun to be with.
This term has been recently popularized by the movie ‘The School of Rock’.
Synonym: bees-knees
“Martin sure knows how to dance, he’s the cats pyjamas, man!”
by Mitch May 31, 2004
2.
cats pyjamas
1920s Lingo describing someone (something) who is great, incredible or special. Usually indicating stylishness or innovation. Pyjamas were a relatively new fashion in the 1920s. The term “cat” was beginning to be used as a term to describe the out going and unconventional jazz-age flappers.
That girl wearing those Paris Hilton sunglasses must think she’s the cats pyjamas.
Those crazy rhinestone studded platinum teeth are the cat’s pyjamas!
by Thomas the Bombest May 10, 2007
So it doesn’t seem to have anything to do with cats, as in felines. Other than cats are so cool that they started a trend in the English language 
I still think that a cat in a pyjamas would be a pretty cool and funny thing to see though
Even cooler would be a set of knitted pj’s. Heh heh