Green’s Dictionary of Slang

cat’s meow n.

also cat’s tonsillitis, duck’s quack, elephant’s tonsils, pig’s scream, sparrow’s chirp
[SE cat + meow; var. on cat’s whiskers n.]
(Aus./US)

1. anything exceptional or superlative.

[US]T.A. Dorgan in Zwilling TAD Lex. (1993) 25: Some party. Some home made hooch. — Gee — I feel like the cat’s meow.
[US]Appleton Post-Crescent (WI) 2 May 9/4: Flapper Dictionary duck’s quack – The best thing ever.
[US]J.T. Farrell ‘Calico Shoes’ in Fellow Countrymen (1937) 33: Mira, she’s the cat’s tonsillitis. [Ibid.] 36: I’m going to bring you all kinds of rubber dresses back from New York, and will they be the cat’s meow.
[US]P. Crosby ‘Skippy’ [comic strip] Lit’rature is the cat’s meow, ain’t it?
[UK]‘Leslie Charteris’ Enter the Saint 167: I call that the elephant’s tonsils.
[US]Wentworth & Flexner DAS.
[US](con. 1916) G. Swarthout Tin Lizzie Troop (1978) 176: ‘Say, that’s the cat’s meow!’ he grinned.
[Aus]N. Keesing Lily on the Dustbin 87: Young people who [...] ‘dress up like a sore thumb’ or ‘the cat’s meow’ are fair game for domestic wits.
(con. 1939) F. Deford in Sports Illus. June [Internet] Billy Conn was the cat’s meow .
[US](con. 1933) G. Pelecanos Big Blowdown (1999) 18: This Chevy, this was the cat’s meow.
in C.G. Appy Vietnam (2006) 106: Go ahead and laugh, but back in ’66 that outfit was the cat’s meow.
[US]K. Greenwald WordWizard Inc. Feb. [Internet] Other sources list ‘[...] the duck’s quack.’.

2. a superior person or someone who poses as such.

[US] in W.C. Fields By Himself (1974) 28: So even if you ain’t the pig’s scream that You say You are, You had a shining example to copy from.
[US]H.C. Witwer Fighting Blood 13: His old man owned the carpet factory here, which seems to make this fathead think he’s the duck’s quack. [Ibid.] 83: The guy which doped that out was the sparrow’s chirp, what?
[US]Wash. Post 25 Jan. SM7: Jargon of the Juveniles Daughter Cat’s meow.
[US]Wentworth & Flexner DAS.
[US]P. Roth My Life as a Man (1974) 293: Peter Tarnopol, you are the cat’s meow.
[US]N. McCall Makes Me Wanna Holler (1995) 104: I thought I was the cat’s meow when I got my first pair of platforms.