Green’s Dictionary of Slang

1. (US) a trunk.

1887

Daily Trib. (Bismarck, ND) 23 Oct. 4/1: A trunk is a ‘bumper’.

2. (US/W.I.) the buttocks [? play on keister n. (1)/keister n. (5)].

1995		Francis-Jackson Official Dancehall Dict. 7: Bumper the behind: u. woman, me love yu bumper/ I love your rear end.
2013		K. Koke ‘Could Have Been’ 🎵 Pretty face, small waist, big bump-per. / Tight pum, firm boobs in her jump-per.
2015		J. Spades ‘Twerk’ 🎵 Gyal dem shakin their bumpers / Twerk, twerk, twerk, twerk, twerk, twerk, turn up.

3. usu. in pl., the female breasts; occas. buttocks.

c.1943		‘Bill O. Lading’ You Chirped a Chinful!! n.p.: Bumpers: Upper front or lower back of a girl.
1948		(con. 1944) N. Mailer Naked and Dead 485: What bumpers on her.
1960		(con. 1950-1960) R.A. Freeman Dict. Inmate Sl. (Walla Walla, WA) 20: Bumpers – a woman’s breastworks.
1966		C. Wood Fill the Stage With Happy Hours (1967) Act IV: Couple of sequins on her bumpers.
1970		‘Red’ Rudensky Gonif 102: Babes with big Bumpers Wanted. For Shipboard Duty.
1977		A. Bleasdale Who’s Been Sleeping in my Bed 48: Those bumpers of hers they’re like the tip ends of torpedoes.
1985		‘Jennifer Blowdryer’ Modern English 77: tits (n): Bumpers.
1988		J. McDonald Dict. of Obscenity etc.
1990		S. Morgan Homeboy 15: Joe rebounded two feet off the fortyfour triple-D bionic bumpers attached to Bermuda Schwartze.
2001		A. Sillitoe Birthday 92: But I still like nudging into your front bumpers.
2005		Jade LB Keisha the Sket (2021) 25: [of the buttocks] I climbed on top of his buff body, wit my bumpa in da air and ma lips on his.

4. (US) the vagina.

1974

G.V. Higgins Cogan’s Trade (1975) 44: I should’ve told her, go out and throw the bumper around.

5. (US prison) in fig. use (see car n. (2)) the status of working for qualification as a gang member, thus phr. on the bumper.

2019

D. Winslow Border [ebook] ‘Whose car are you in?’ ‘I’m doing my bones with Eme now.’‘If this works out [...] I’ll try to get you off the bumper’ [Ibid.] Slicing up Nico gets him to a prison [...] and he goes in already on the bumper to get into the Mara Salvatrucha car by killing a Calle 18.