How to understand "cat's evening wear"?
Aside from two matches to a Tumblr page with the name "The Cat's Evening Wear," a Google search returns the following six readable matches for the phrase. From a September 8, 2004, post at RoadbikeReview.com:
My SO is the cat's evening wear, but useless when it comes to bike related anything.
From a September 21, 2006, comment posted at Threadless.com:
Esoteric humor is the cat's evening wear.
From a September 29, 2008, comment posted at Aberdeen-Music.com:
I'm all about Micah P Hinson today. His cover of Yard of Blonde Girls is the cat's evening wear.
From a June 29, 2009, comment posted at InsideSTL.com:
Drumsticks are the cat's evening wear. I like the ones with crushed peanuts on them.
And from a July 17, 2015, post at github.com:
We've seen what pure functions are and why we, as functional programmers, believe they are the cat's evening wear.
What these instances have in common is obvious admiration for the thing they identify as the cat's evening wear. This reflects a clear kinship to "the cat's pajamas" (presumably later-in-the-night cat's wear). J.E. Lighter, Random House Dictionary of Historical Slang (1994), has this entry for cat's pajamas, which it finds instances of going back to 1922:
cat's pajamas n. something that is extraordinary, esp. splendid or delightful.—constr[ued] with the. {Unlike CAT'S MEOW, this phrase sometimes expresses annoyance or amazement.}
Barbara Kipfer & Robert Chapman, Dictionary of American Slang, fourth edition (2007), reports that "cat's pajamas" is itself a variant of "cat's meow" and that both terms mean the same thing: "Something or someone that is superlative." It also offers this note on the origin of the phrase:
{1920+; the entry form [cat's meow] and pajamas are said to have been coined by the cartoonist and sports writer Tad Dorgan, who died in 1929}
The main emotion associated with "the cat's evening wear" is delight, and that seems true of "the cat's pajamas," as well. The few online matches for "the cat's evening wear" suggest that it remains a relatively rare variant of "the cat's pajamas," but anything can happen in the world of slang.