Green’s Dictionary of Slang

bee’s knees n.

also bullock’s bollocks, cuckoo’s chin, duck’s nuts, elephant’s (fallen) arches, elephant’s manicure, gnat’s elbow, nit’s tits, owl’s bowels, snail’s ankles, snake’s hips, ...toenails, turkey’s elbow, turtle’s neck, worm’s ribs
[nuts n.2 (1)]

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

[[Aus]Duke Tritton’s Letter n.p.: I’m teaching Mary and all the Tin Lids in the district to Dark An’ Dim, and they reckon I’m the bees knees, ants pants and nits tits all rolled into one].
Woolwich Gaz. 5 July 4/7: There is one place [...] where this delicious edible [i.e. Scotch shortbread] can be had in its proper crispness and flavour [...] The real ‘bee’s knee’, it is.
Uncle Sam 1 Jan. n.p.: Leiut. McNamara is the bee’s knees when it comes to drilling,. 1-2-3-4, hep, hep, tell the sergeant to get in step. What he doesn’t know about drilling isn’t worth while knowing.
[US]Washington Times (DC) 8 Oct. 48/2: Europe may be the bee’s knees to the Europens, but [etc.].
[US]H.C. Witwer Fighting Blood 101: You’re the bee’s knees, for a fact! [Ibid.] 111: If I ain’t the turkey’s elbow when I’m inside this bathrobe, then there’s only two Frenchmen in Paris the year round!
[US]Reading Times (PA) 12 Feb. 4/3: My sweetie’s a high-brow and knows his groceries. He’s the worm’s ribs .
[US]R. Fisher Walls Of Jericho 181: Well, this Joshua thought he was the owl’s bowels.
[UK]D.L. Sayers Have His Carcase 195: ‘Ain’t she the snail’s ankles?’ asked Mr. da Soto, admiringly.
[US]J. Sayles Union Dues (1978) 145: He thinks Pancho Villa is the bee’s knees.
[UK](con. 1960s) G. Byrne Pictures in my Head 7: All the neighbours are out for a gawk at my brother and they all think he’s the bee’s knees.
[UK]Indep. Mag. 28 Aug. 6: I thought I’d look like the bee’s knees in white.
[UK]K. Sampson Outlaws (ms.) 82: Fucking loves our Gerrard, he does. Thinks he’s the bee’s knees.
[Can]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.
[UK]V. McDermid Insidious Intent (2018) 219: ‘She thought he were the bee’s knees’.

2. of things, the best, the superlative.

[US]Appleton Post-Crescent (WI) 28 Apr. 17/4: bees knees – Peachy, very nice. Sometimes known as ‘The Berries’.
[US]H.C. Witwer Fighting Blood 235: Spence thinks my scheme is the gnat’s elbow.
[US]Wash. Post 25 Jan. SM7: No noon hour on the college campus or in the office lunchroom would be complete without the words: [...] ‘the bee’s knees,’ ‘the snake’s hips,’ ‘the elephant’s manicure,’ not to speak of the ‘tadpole’s teddies.’.
[US]F. Walter Pollock ‘The Current Expansion of Sl.’ in AS II:3 145: We find [...] ‘snake’s toenails’.
[US]Wood & Goddard Dict. Amer. Sl. 10: elephant’s fallen arches, snake’s hips, etc. Something excellent.
[US]M. Levin Reporter 55: [running head] Bee’s Knees Nothing To These.
[UK]Post (Lanarks) 23 Apr. 6/2: The alligator’s adenoids, the bee’s knees, [...] the butterfly’s boots, the caterpillar’s kimono, the duck’s quack, eel’s hips, elephant’s eyebrows, gnat’s whistle [...] oyster’s ice skates, pig’s wings. They all mean top notch in Chatanooga!
[US]R.P. Smith ‘The Goofy Girls’ in Russell Permanent Playboy (1959) 140: ‘Was it ever an evening! I mean to tell you.’ ‘The bee’s knees,’ she’ll say, and giggle.
[UK]J. McClure Spike Island (1981) 276: I was put into a CID office and I took to it like a duck to water. I thought it was the bee’s knees.
[UK]Indep. Mag. 4 Dec. 67: It’s the bee’s knees – I had a grin from ear to ear driving this.
Parkinson & Green Cutting It Fine (ms.) 64: A new British sausage restaurant [...] it was going to be the bee’s knees, it was going to be the nuts.
[US]K. Greenwald WordWizard Inc. Feb. [Internet] Other sources list ‘[...] the gnat’s elbow, the elephant’s (fallen) arches, [...] the cuckoo’s chin, [...] the turtle’s neck’.
[NZ]McGill Reed Dict. of N.Z. Sl. 69: duck’s nuts, just the Very desirable, a variant of ‘the bee’s knees’. ANZ.
[UK]D. Mitchell Black Swan Green 74: That were the bullock’s bollocks.
[UK]Observer Mag. 30 Sept. 10: Whereas once a sneeze was something thought to displease [...] for an increasing amount of people it’s the bee’s knees.