Green’s Dictionary of Slang

1. (also sloppy thirds) sexual intercourse with a woman (occas. man) who has had another partner/partners immediately previously, whether forced or voluntary.

1966		M. Rumaker Exit 3 and Other Stories 53: ‘G’wan,’ said Jim, pushing the sailor toward the woman. ‘I don’t mind sloppy seconds.’.
1974		J. Lahr Hot to Trot 171: I’m not taking sloppy seconds. I’ve never been second in anything.
1981		H. Gould Fort Apache, The Bronx 327: Yeah, it would be pretty embarrasing to have sloppy seconds on your own old lady.
1982		W. Wharton Midnight Clear 39: [We] would decide the ‘pecker order,’ so we matched coins. Morrie won, Shutzer second, me for sloppy thirds.
1997		G. Sikes 8 Ball Chicks (1998) 146: We’ve pulled trains a couple of times. I’m always first. I ain’t taking sloppy seconds.
2001		S. King Dreamcatcher 343: Just wondering if you got your share of that girl – you know, the one Frankie broke in. Did he give you sloppy seconds?
2001		see sense 2.
2012		(con. 1980s) I. Welsh Skagboys 55: Half ay fuckin Leith’s [...] claimin thuv been in thaire pumpin away oan Franco’s sloppy fuckin seconds.
2012		J.D. Hibbits ‘The First day of Hell Week’ in ThugLit Dec. [ebook] Sloppy seconds with his father’s whore.
2017		T. Pluck Bad Boy Boogie [ebook] ‘[He] taught her the art of the blow job [...] on the rides home. Hope you enjoyed our sloppy seconds’.
2022		J. Hannaham Didn’t Nobody Give a Shit 187: At least when your butt look like 9/11 happened up in there, won't nobody be coming back for seconds that sloppy!

2. the woman who is participating in this sequential sex.

2001

K. Albertson Lali’s Passage 202: Tim mumbled something about not wanting ‘sloppy seconds’. Lee thought to enlighten him that these ladies were always ‘sloppy seconds’.

3. (US gay/prison) the man who participates second or later in sequential sex.

1972

B. Rodgers Queens’ Vernacular 155: The first to gain anal entrance, a highly prized honor, is called the welcome wagon. The second in line is sloppy seconds, while the third fucker is bloody thirds (no other slang terms are used after thirds, probably because the prize is such a mess by then).