Green’s Dictionary of Slang

snapper n.⁴

the penis.

c.1864		‘I’d Choose to be a Baby’ in Rakish Rhymer (1917) 158: The girls would feel my snapper, / They’d kiss it and they’d vow / ’Twas sweet as any sugar—.
1890–1904		Farmer & Henley Sl. and Its Analogues.
1951		in E. Cray Erotic Muse (1992) 287: Now my prick is starting to feel funny. / Hoist your ass and wiggle your tits / Till the great big snapper spits. / Cherry, bye, bye.