Green’s Dictionary of Slang

sour grape n.

(Aus./N.Z. Und.) a rape; also as v.

1982		G. Newbold Big Huey 254: sour grape (v) Rape.
1988		McGill Dict. of Kiwi Sl. 106/1: sour grape rape; eg ‘He got seven years for sour grape.’ Underworld.
1990		Tupper & Wortley Aus. Prison Sl. Gloss. 🌐 Sour grape. Rhyming slang for rape.
1999		D. Looser ‘Boob Jargon’ in NZEJ 13 35: sour grape v. (To) rape.
2001		D. Looser Boobslang [U. Canterbury D.Phil. thesis] 173/1: sour grape n. 1 rape [...] sours n. pl. rape [...] sour grape v. to rape.

In derivatives

sour graper (n.)

a rapist.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 173/1: sour graper (also sour grapist) n. a rapist (raper).