Green’s Dictionary of Slang

1. (US short-order) pork chops.

1908

Commercial (Union City, TN) 22 May 5/1: Ever see a Jew walk in [...] and whisper that he wants an order of pork chops? Here’s what we tell the cook: ‘Forbidden fruit, put out the lights and chase the rabbi’.

2. (Irish) the ‘Adam’s apple’ in the throat.

1943		(con. c.1900s) G.A. Little Malachi Horan Remembers 146: He tried to brazen it out. But I seen his ‘forbidden fruit’ and it lepping in his neck.
1986		P. O’Farrell Tell me, Sean O’Farrell 23: His forbidden fruit (Adam’s apple) was leppin’ with rage.

3. an underage sexual partner of either sex.

1949		Monteleone Criminal Sl. (rev. edn) 89: forbidden fruit [...] a young virgin.
1979		Maledicta III:2 220: Princess (younger than a queen) is camp, and jailbait and forbidden fruit are hardly applicable in countries where the age of consent is very low.
1989		H. Rawson Dict. of Invective (1991) 157: A person—male or female—beneath the legal age of consent is forbidden fruit.