Green’s Dictionary of Slang

nasty n.

[in sexual contexts an acknowledgment, if not an agreement, with the Western ambivalence as regards sexuality; note Williams (1994) for 17C use of nasty as ‘bedfellow’]

1. anything unpleasant, varying as to context (cf. nasties n. (3)).

[US]R. Chandler ‘Trouble Is My Business’ in Spanish Blood (1946) 203: He has just collected ten from your iron man for slipping me the nasty.
[UK]Observer Screen 9 Jan. 11: The ‘video nasties’ scandal of the early Eighties.

2. anyone unpleasant, threatening or scary; often in pl.

[UK]Eve. Teleg. (Dundee) 26 Dec. 6/3: Heinie Himmler’s a dirty clype, and Joey Goebbels broadcast tripe [...] Lot of nasties.
A.P. Herbert Let Us Be Glum 25: So on, gallant greeks! crush and capture and slay, the Nasties, the Dirties, who stand in your way.
Sat. Night Feb. 27: They’ve always been around, the Nasties—disguised as merely unpleasant people, as persons with hateful, mean, offensive characters.
[US]W.C. Anderson Bat-21 135: The nastys decided on a quick, massive attack to crush the South Vietnamese.
[US]H. Harrison Bill [...] on the Planet of Robot Slaves (1991) 115: You’ll find the nasties who shot us down.
[Ire]P. McCabe Breakfast on Pluto 171: Ending up being hung from the rafters by the tootle with all those nasties poking blades into her pale white flesh.
[UK]K. Sampson Powder 337: Wheezer knew there were no nasties lurking in the gang, no racists or homophobes.
[UK]Observer Mag. 14 May 19: Bill had ‘called the knock’ on many heavy-duty nasties, including a number of Turkish heroin traffickers.

3. the vagina.

[Aus]B. Humphries Barry McKenzie [comic strip] in Complete Barry McKenzie (1988) 45: I’m as dry as a nun’s nasty.
[NZ]McGill Reed Dict. of N.Z. Sl.

4. the penis.

[Aus]B. Humphries Barry McKenzie [comic strip] in Complete Barry McKenzie (1988) 17: The only time anything like that’s ever happened before was when I was a nipper and the scoutmaster flashed his nasty!
[UK]‘John le Carré’ Constant Gardener 477: Groping her tits. Pressing his nasty up against her crotch.

5. sexual intercourse; thus do the (big) nasty

[US]E. Folb Runnin’ Down Some Lines 247: nasty, the Sexual intercourse.
[US]R.C. Cruz Straight Outta Compton 64: He wasn’t about to take any gump from a so-and-so self-proclaimed homicide officer who had done the nasty with a white girl.

In phrases

do (someone) a nasty (v.)

to do something unpleasant (to someone), to cause (someone) trouble or problems.

[US]E. Torres After Hours 188: Last time out with you, you did a nasty.
[UK]J. Healy Streets Above Us (1991) 22: Central Finance have done a nasty, slapped a D notice on us.
G. Miller ‘The Relic’ FanFic on Doctor Who The Legacy [Internet] Nick gripped the hilt firmly and delicately felt the edges and the break in the blade. “You mean other than that it’s broken but you could still do someone a nasty with it?”.
do the (big) nasty (v.)

1. (orig. US) to have sexual intercourse.

[US]Frank Zappa ‘Brown Shoes Don’t Make It’ [lyrics] She’s a teenage baby and she turns me on / I’d like to make her do her nasty on the White House Lawn.
[US]G. Tate ‘A R Kane’ in Flyboy in the Buttermilk (1992) 111: Shug [...] describes it to Celie as ‘a little button’ that gets so hot it melts when you’re doing the nasty properly.
[UK]T. Fontana and D. Sarjeant ‘Animal Farm’ Oz ser. 2 ep. 7 [TV script] Who’d have thought about you doing the nasty.
[NZ]P. Shannon Davey Darling 51: Oh, you mean have sex, do the nasty with another woman? But how?
‘Chelsea G. Summers’ in Hazlitt.net 8 Jan. [Internet] We don’t have sexual intercourse—we ‘get busy,’ ‘hit it,’ ‘do the nasty,’ ‘get some,’ ‘score,’ and perform countless other acts that we refer to by adorable, horrifying, and illuminating turns of phrase.

2. (US black) to perform cunnilingus.

[US]E. Folb Runnin’ Down Some Lines 154: One of the expressions for oral sex is to do the nasty.
flash one’s nasty (v.)

(N.Z.) to expose one’s genitalia.

[NZ]McGill Reed Dict. of N.Z. Sl. 79: flash your nasty A lewd request for a woman to expose her genitals, or a man flashing his genitals without being asked. ANZ.
have a bit of (old) nasty (v.)

to have sexual intercourse.

[US]‘J.M. Hall’ Anecdota Americana II 55: I ain’t had a bit of nasty in four months and it would go fine.
[US] joke cited in G. Legman Rationale of the Dirty Joke (1972) I 174: We went upstairs [...] and had a bit of old narsty.