Green’s Dictionary of Slang

very effeminate.

1964		Lavender Lex. n.p.: nelly:– [...] anything that is overtly homosexual, or questionable.
1965		L. Bruce How to Talk Dirty 34: He was so obviously nellie.
1972		E. Newton Mother Camp 33: The nellie male homosexual and the butch lesbian.
1978		R. Price Ladies’ Man (1985) 51: A real nelly faggot came to the door.
1988		(con. 1940s) C. Bram Hold Tight (1990) 72: Just nelly crap from a nelly nigger.
1993		T. Jones Pugilist at Rest 83: ‘You mean I don’t have to get a haircut after all?’ I said in my best nellie voice.
2004		A. Kleinzahler Cutty one Rock (2005) 184: I remember him turning up [...] on acid with a couple of the nelliest faggots you could imagine.
2005		E. White My Lives 142: The prettiest nelly boys attract, it seems, mostly nutty straight men who [...] want a chick with a dick.
2018		Financial Times ‘How to Spend It’ 1 June 🌐 The carabiner clips on the business bags (price on request) are a ‘bit Nellie’ (Blahnik for overly feminine and fussy).