Green’s Dictionary of Slang

1. anything exceptional, superlative.

[1921		Brooklyn Dly Eagle (NY) 8 July 20/5: [headline] ‘Cat’s Pajamas’ New Dance, Not Nightie, Lands Two in Jail] .
1921		Bridgeport Teleg. (CT) 14 Sept. 12/4: Speaking about drummers, wasn’t Howard Goulden the cat’s pajamas at the Sousa concert.
1922		Appleton Post-Crescent (WI) 29 Apr. 7/2: Flapper Dictionary cat’s pajamas – Anything that is very good.
1922–24		O.O. McIntyre White Light Nights 103: Hot diggedy dog! [...] This town is sholy the cat’s vest. Colored folks is quality.
1923		H.C. Witwer Fighting Blood 72: Two-Punch Jackson [...] called my right hook to the jaw ‘the cat’s cuffs!’ [Ibid.] 85: I tried to sell the world the idea that it was thirsty and that the stuff I had on tap was the kitten’s vest when it comes to quenching. [Ibid.] 354: John L. Sullivan figured himself the clam’s garters.
1924		P. Marks Plastic Age 102: It’s a goddamn good poem. It’s the cat’s pajamas.
1925		R. Lardner ‘Mr. and Mrs. Fix-It’ in Coll. Short Stories (1941) 411: But the cat’s nightgown is Tom Stevens and his wife! They’re the team that wins the Olympics!
1927		Eve. Teleg. (Dundee) 8 Sept. 3/2: He certainly showed good and pretty that he was the caterpillar’s camisole and antelope’s tonsils all right.
1930		‘Leslie Charteris’ Enter the Saint 126: ‘It sounds good,’ he said. ‘It’s the caterpillar’s spats!’.
1931		V. Carter ‘University of Missouri Sl.’ in AS VI:3 203: cat’s pajamas: term of extreme eulogy.
1936		N. Marsh Death in Ecstasy 122: Why, he thinks I’m the sandfly’s garters.
1947		S.J. Perelman ‘No Dearth of Mirth’ in Keep It Crisp 83: It’s the cat’s pyjamas – a peachamaroot!
1955		Mad mag. Jan. 5: Sale [...] Alligator shoes, Cat’s pajamas, Monkey suits.
1960, 1975		Wentworth & Flexner DAS.
1999		N. Stephenson Cryptonomicon 884: I knew it wouldn’t be so great for you. But for me it’s the cat’s pajamas.
2001		OnLine Dict. of Playground Sl. 🌐 cat’s pyjamas n. something excellent or wonderful.
2003		K. Greenwald WordWizard Inc. Feb. 🌐 Other sources list ‘the kipper’s knickers [...] the caterpillar’s kimono.’.
2018		(con. 1963) L. Berney November Road 42: ‘Well, if that ain’t the cherry on top of my sundae [...] After the day I had, it’s the damn cat’s pajamas’.

2. used sarcastically, a joke, a ‘laugh’.

1920		Gasconda Co. Republican (Owensville, MO) 30 May 7/3: Suitor: I have long loved your daughter — and I want to make her my wife. Wealthy Man: But I have no daughter. Suitor: Cat’s Pajamas — They told me you had a daughter.
1925		R. Lardner ‘The Love Nest’ in Coll. Short Stories (1941) 207: ‘You’re not used to it?’ ‘Not used to it! That’s the cat’s pajamas! Say, I’m like this [i.e. drunk] half the time, see?’.

3. a superior person, or someone who poses as such.

1922		Morn. Tulsa Daily World (OK) 17 Dec. 74/5: Hyah’s the cat’s pajamas.
1924		T. Thursday ‘A Lodging for the Knight’ in Top-Notch Mag. 1 Apr. 🌐 [He] ain’t exactly the lion’s bathrobe when it comes to great wealth.
1925		S. Lewis Arrowsmith 445: This kid used to think Pa Gottlieb was the cat’s pajamas.
1928		(con. WWI) H.F. Cruikshank ‘So This Is Flanders!’ Battle Stories July 🌐 He turned out the cat’s Mac after we got him trained.
1936		M. Levin Old Bunch (1946) 31: Is he the cat’s pajamas!
1937		P. Cheyney Dames Don’t Care (1960) 91: Make a big play for me an’ tell me that I am the cat’s lingerie.
1958		E. Dundy Dud Avocado (1960) 107: I thought we band of brothers were absolutely the cat’s pyjamas.
1982		R. Dahl Revolting Rhymes n.p.: You are the only one to charm us, / Queen, you are the cat’s pyjamas.
2000		W.T. Vollmann Royal Family 225: Aren’t you the cat’s pajamas?
2010		S. Mayberry Her Best Friend 174: That’s how I feel. I think you're the bee’s knees. The cat’s pajamas. The ant’s pants.