Green’s Dictionary of Slang

dozen n.

[backform. f. dozens n.]

(US black) a ritual insult.

[US]W.C. Handy ‘Gouge of Armour Avenue’ [lyrics] For though she slipped him in the dozen only this from him I heard: ‘Oh, oh, Baby, Hold your tongue’.
[US]E. Folb Runnin’ Down Some Lines 12: I would run down the latest ‘dozen’.