Green’s Dictionary of Slang

1. a homosexual.

[1972		B. Rodgers Queens’ Vernacular 66: Dorothy and Toto 1. gay boy and his dog 2. dominating effeminate homosexual man with his paid-for escort 3. extended to any male couple whose effeminate partner is in command].
1986		Sydney Morn. Herald 5 Apr. 149/10: [personal advert] Arcadia, quiet friend of Dorothys to share large home on acres [Simes:DLSS].
1988		Capital Gay (London) 12 Feb. 11/3: A Somewhere-Over-The-Rainbow Coalition..offers little to the friends of Dorothy because, like the Wizard of Oz, its power is illusory [OED].
1991		W.S. Gilbert Spiked 200: [W]e thought you were normal. We didn’t know that you were so. We didn’t know that you were musical. We didn’t know that you were a friend of Dorothy’ [Simes:DLSS].
1995		A. Heckerling Clueless [film script] Yo, look. Are you bitches blind or something? Your man, Christian is a cake-boy! [...] He’s a disco-dancing, Oscar Wilde-reading, Streisand ticket-holding friend of Dorothy, know what I’m saying?
1995		P. Scott One Dead Diva 205: He couldn’t have heard about the Friends of Dorothy party, surely! [Simes:DLSS].
1996		(ref. to 1961) Philip Bockman in Boys Like Us 75: We even had a password, by which we identified ourselves in those days when very few dared to be ‘obvious’: ‘I’m a friend of Dorothy’s.’ If people didn’t get it, you knew they weren’t gay. A gay person would answer, ‘I am too’ with a knowing smile.
2000		Indep. Rev. 24 Jan. 8: When your airline is a friend of Dorothy’s [...] The travel business now realises that gay customers are a profitable niche in the market.
2002		P. Scott It’s about your Friend 2002: ‘I’ve never discussed my sexuality in the office.’ ‘Very wise. Why should you? .. People only use it as a weapon against you. I should know. I’m a dear friend of Dot’s myself’ [Simes:DLSS].
2004		Guardian Weekend 7 Aug. 31/1: Those were the days when gay punters had to ‘knock twice and ask for Dorothy’.
2011		Eve. Standard 14/3: Bachmann, a ranting homophobe [...] is widely rumoured on the Internet to be himself, something of a ‘friend of Dorothy’.
2013		slate.com 19 June 🌐 Revealing men’s swim garments are, for the U.S. consumer, irrevocably associated with ‘foreigners’ and, most terrifying of all, friends of Dorothy.
2014		P. Cramp On My Gaydar 14: When you go to the ballroom / do you dance at which end? / I can’t figure out / if you’re Dorothy’s friend.
2016		Twitter 17 May 🌐 So one of the furniture delivery gentlemen admired our portrait of Judy Garland. Wonder if he’s a friend of hers, so to speak.

2. as sense 1 substituting Dorothy by a ref. to a well-known gay man.

1999		S. Selvadurai Cinnamon Gardens 111: ‘Surely you could tell, couldn’t you?’ ‘Tell what?’ Belandran said [...] ‘They’re, you know...inverts. “Friends of Oscar” [i.,e. Wilde]:, as Aunty Ethel used to say’ [Simes:DLSS].
2010		N. Drinnan Rare Bird Truth 118: ‘There’s a lot of things you don’t know about Jasper Bresda-Khan… Firstly he’s a batty boy, a horse’s hoof, a friend of Quentin’s [i.e. Crisp]’ [Simes:DLSS].