Green’s Dictionary of Slang

real McCoy, the n.

also the real (Sandy) Mackay, ...McKay, ...McKie, ...McKoy, McCoy, the McCoy, the M’Coy
[a variety of popular etymologies have focused on the fighting name of Norman Selby ‘Kid’ McCoy (1873–1940), welterweight champion (1898–1900) and sometime strike-breaker or ‘scab-herder’ for the Ford Motor Co. Ironically, Selby was not in fact the real McCoy, this was another, slightly older welterweight, Peter McCoy, who toured with John L Sullivan c.1885 and who killed himself after a bad loss. However the Scot. National Dict. (1870) notes that the saying, albeit spelt ‘McKay’ was adopted in 1856 (see cit.) by Messrs G Mackay and Co, whisky distillers of Edinburgh, as their advertising slogan. A further citation, as the ‘real Sandy McKay’, is found in 1873 – both Scottish uses are substantially earlier than the boxing attribution, although this may well have broadened the usage]

1. (orig. US) the genuine article, the ‘real thing’.

‘Young Glasgow’ Deil’s Hallowe’en 25: A drappie [i.e. drop] o’ the real MacKay.
[UK]A. Wingfield ‘The Real Sandy Mackay’ Poems and Songs 62: Faith without wark / Shows ye’re still in the dark, / For it’s no’ the real Sandy Mackay. * [...] He’s not worthy your care, / For he’s no’ the real Sandy Mackay. * [note] An expression used in some parts of Scotland, equal to saying ‘it is not the real thing’.
[[Aus]Bulletin (Sydney) 21 Mar. 6/2: A Melbourne paper says that ‘a subscription is being raised in Hobart to remunerate Mr. Matthew Burnett for his self-sacrificing work in the cause of temperance.’ And very proper too. We shall be proud to contribute a bottle of the real old Mackay (kept specially for the regalement of temperance lecturers who do us the honor to call on us) to the fund. [...] He should not be expected to get thoroughly sober for the rest of his life].
[Aus]Stephens & O’Brien Materials for a Dict. of Aus. Sl. [unpub. ms.] 103: MACKAY, THE REAL: pronounces Muckeye: slang term to denote absolute genuineness of purity. A dram of really good spirits would be spoken of as ‘a drop of real Mackay.’ The real thing itself, unadulterated and unsophisticated.
[UK]Boy’s Own Paper 4 May 484: Giving it a good ring to show it was the real McCoy.
[Aus]J. Furphy Such is Life 211: [This] made us feel the station aristocracy to be a mere bourgeoisie, and ourselves the real Mackay.
[US]T.A. Dorgan in Zwilling TAD Lex. (1993) 68: I heard the boss say you dolled up and looked like the real McCoy.
[Aus]Cairns Post (Qld) 3 July 4/7: Who has not heard the men from the land o’ cakes say ‘The Real Mackay’ when anything appeals to them.
[US]P. & T. Casey Gay-cat 156: It’s the real McCoy, thet idee.
[US]J. Lait Gangster Girl 25: You look the real McCoy, Annie.
[Aus]T. Wood Cobbers 117: Gold. The Dinkum Oil, as they say here. The Real Mackay.
[US]F.S. Fitzgerald ‘Teamed with Genius’ in Pat Hobby Stories (1967) 70: He was nothing less than the real McCoy.
[US]W. Winchell On Broadway 21 Feb. [synd. col.] Jane Pickens Waldorfing in a little number with diamond shoulder straps. The M’Coy!
[US]M.H. Boulware Jive and Sl. n.p.: Real McKoy ... Just the thing.
[US]W.R. Burnett Asphalt Jungle in Four Novels (1984) 130: This was the McCoy.
[Aus]D. Walker We Went to Aus. 48: This rum, and this rum alone, was ‘the Real Mackay’.
[US]‘Big Bill’ Broonzy ‘I Wonder When I’ll Get to be Called a Man’ [lyrics] When Uncle Sam called me, I knowed I’d be called a real McCoy.
[Aus]D. Stivens Jimmy Brockett 198: It was the real McKie he was giving me.
[US]J. Jones From Here to Eternity (1998) 675: If he doesnt cool off in 21 days [...] then they figure its the McCoy and he’s not acting.
[Aus]H. Drake-Brockman ‘The North-west Ladies’ West Coast Stories 157: What about Matron? She’s been the real Mackay, in her day.
[US]T.I. Rubin In the Life 102: Instead of the McCoy, sometimes you get nothing but plain straw.
[US]K. Brasselle Cannibals 278: The city desk [...] and the phones were the real McCoy.
[US]G.V. Higgins Friends of Eddie Coyle (1973) 78: Far as I know it’s the McCoy. You want to count it?
[UK]P. Theroux Picture Palace 254: She was just another double [...] but nevertheless bearing traces of the real McCoy.
[US]Grand Master Flash ‘Scorpio’ [lyrics] Cowboy is the real McCoy.
[UK]M. Frayn Now You Know 120: Jacqui’s gazing at me – she knows this is the real McCoy.
[US](con. 1949) G. Pelecanos Big Blowdown (1999) 138: I like Robert Ryan. Ryan’s the McCoy.
[UK]B. Hare Urban Grimshaw 195: Molly thought she was training Urban up and so he didn’t yet qualify as the real McCoy.
[Aus]N. Cummins Tales of the Honey Badger [ebook] He dropped the plastic [buttocks] and let the crowd have it with the Real McCoy.

2. (US) money.

[US]T.A. Dorgan in Zwilling TAD Lex. (1993) 68: (Mr Wise Returns From Lunnon) Waitin fer ‘McCoy’ from home.
[US]T.A. Dorgan in Zwilling TAD Lex. (1993) 68: (Handicap Horses Tell TAD Secrets) Plant your McCoy where its bound to get bigger.