Green’s Dictionary of Slang

in pl., the testicles; thus long plum, the penis.

1613		Middleton Chaste Maid in Cheapside III ii: They’ve [...] cull’d out All the long plums too, they’ve left nothing here But short wriggle-tail comfits.
1618		Fletcher Loyal Subject IV ii: Mistris, You are to suffer your penance some half hour hence now. How far a fine Court Custard with Plums in it Will prevail with one of these waiting Gentlewoman.
a.1640		R. Brome New Academy II i: I’ll ask her If she can speak with plums in her mouth; and then I’ll offer her a long one and two round ones.
1654		T. Killigrew Thomaso Pt 1 I iv: Thou lovest him, ... whether for taking thy Maiden-head, or giving thee Plums. [Ibid.] I v: If he go into her house she has all she desires; and will either pluck his Plums by flattery, or else so shake and cudgel the Tree, he’l be glad to let them fall.
c.1864		‘The Idiot Boy’ Rakish Rhymer (1917) 33: When from your pocket you look out a stem where hung two plums. [...] And after she had suck’d the plums she tried to crack the stones.
1934		‘J.M. Hall’ Anecdota Americana II 97: J stands for Jockstrap / To hold up the plums.
1981		A. Bleasdale Missile Market [TV play] 13 Jan. A kick in the plums.
1989		Viz June/July 14: Ooh, my poor plums!
1997		Roger’s Profanisaurus in Viz 87 Dec. n.p.: plums n. Knackers; balls; testicles. Together with melons and large pairs, the source of much mirth in British fruit shops.
2000		Guardian Rev. 19 Feb. 12: Hoary old favourites such as, Greengrocer: ‘Would you like to squeeze my plums?’ Nigel: ‘I don’t think that will be necessary.’.
2013		T. Robinson Hard Bounce [ebook] ‘Shame on you [...] And your plums.’ [...] ‘Leave my plums out of this’.