Green’s Dictionary of Slang

dozens n.

also dirty dozens, dozen, snagging
[f. the throw of twelve in craps, the worst possible throw, or f. its folk origins as a set of ritualized verses, usu. in rhymed couplets, which ran through twelve specific sexual acts, each rhyming with the numbers one to twelve; dozens can be ‘dirty’ or ‘clean’, depending on the level of obscenity involved; otherwise unsupported, Legman, The Rationale of the Dirty Joke (1968), suggests ‘possibly from the Saxon word “doze”, to stun or overwhelm, as in bulldozer’; for an extended discussion of ety. see E. Wald Talking ’Bout Your Mama (2012)]

[1910s+] (US black) a ritual game of testing a rival’s emotional strength by insulting his various relatives, esp. his mother, and taking similar insults in return; the insults are usu. sexual and/or scatological; thus the common addition of the adj. dirty; also attrib.

In phrases

play the dozen(s) (v.) (also play dozen, put in the dozen, shoot the dozens, slip (in) the dozens, slip in the twelves) [1910s+] (US black)

to compete in ritualized mutual insults, often about one’s family.

play the dozens with one’s uncle’s cousin (v.)

[1940s] (US black) to go about things in quite the wrong way, to make a mess of things.

put someone in the dozen(s) (v.)

[1920s+] (US) to put somone in a negative situation.