Green’s Dictionary of Slang

ding-dong n.3

(US) the penis.

[US]‘Old Gingerbread’ in Bawdy N.Y. State MS. n.p.: One hand grasped a knife, and the other my old ding dong, / And off came old ginger bread nine inches long.
[US]PADS 2.29: Ding-dong [...] the penis.
[US]Southern & Hoffenberg Candy (1970) 153: I dug the de-frocked ding-dong of his which I’ve no doubt you know only too well!
[US]Velvet Undergound ‘Sister Ray’ [lyrics] She’s busy sucking on my ding-dong.
[US]L. Kramer Faggots 233: Naked sprites, their ding-dongs bouncing up and down.
[US]O. Hawkins Chili 42: Gino had [...] a small ding dong.
[US]N. Kelley ‘The Code’ in Brooklyn Noir 187: ‘King Kong with a powerful ding-dong!!!’ he roared.