Green’s Dictionary of Slang

1. manual stimulation of the female genitals by the middle finger.

1945		in G. Legman Limerick (1953) 277: While I’ll own that stinkfinger’s amusing, / Still, this constant delay / Tends to hold up the play, / And this goom on the deck’s most confusing.
1964		P. Terson Night to Make the Angels Weep (1967) I ii: It’s not going to be like that – whilst ’Oskie and me harrk to your snores of sweet stinky finger – not a bit of it.
1978		J. Webb Fields of Fire (1980) 239: And the next time you’ll want to cop a feel, maybe get a stinky finger. And after that you’ll want a ride.
1983		N. Proffitt Gardens of Stone (1985) 119: They would [...] work on getting drunk or getting a little stink-finger.
2001		I. Welsh Glue 39: Ah settles her doon oan the couch giein her the stinky-pinky for a bit, sliding ma hand up that wee kilt and inside her pants.
2001		D. Looser Boobslang [U. Canterbury D.Phil. thesis] 178/1: stink finger n. 2 a fondle with one’s partner during visits.
2012		(con. 1980s) I. Welsh Skagboys 27: Ah’m giein this burd the stinky pinky.

2. a gesture with the raised middle finger (the remaing digits are curled)[its use in sexual foreplay].

1996

J. Byrell Lairs, Urgers & Coat-Tuggers 251: [He] gives him the old stink-finger sign, resigns on the spot and toss the apron in the slops bucket and strides out the bar doors.

3. (N.Z. prison) an officer who performs rectal examinations.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 178/1: stink finger n. l a prison officer who conducts internal searches of inmates.