Green’s Dictionary of Slang

anything or anyone repellent, whether physically (esp. sexually) or emotionally.

1965		Lancaster New Era (PA) 12 Oct. 12/6: Teen-Age Vocabulary — ‘ITO’ is Instant Turn Off.
1978		L. Kramer Faggots 18: Sagging tits, a definite turn-off.
1985		B. Humphries Traveller’s Tool 41: That’s a real turnoff.
1993		I. Welsh Trainspotting 141: Renton [...] tried to imagine that he was shagging Margaret Thatcher, Paul Daniels [...] Jimmy Savile and other turn-offs.
1998		A. Warner Sopranos 154: See that, townies with a fucking suit on; what a turnoff.
2005		E. White My Lives 122: There’s nothing that’s more of a turnoff than intelligence.
2010		A. Steinberg Running the Books 230: The fact that one of the strongest characters [...] was a sex offender was a major turnoff.
2016		‘Chelsea G. Summers’ in Hazlitt.net 8 Jan. 🌐 Cochran [...] became the first playmate to have her photos accompanied by a questionnaire divulging her ‘turn-ons’ (Corvette sports cars) and ‘turnoffs’ (fresh guys).