Green’s Dictionary of Slang

not worth a damn phr.

also ...a continental damn, ...a dam, ...a darn, ...a drat
[damn n.]

a negative phr. used to imply uselessness or incompetence; thus occas. antonym worth a damn, valuable, worthwhile (see cit. 1957); see also under worth a... phr.

[UK]T. Creevey letter 18 Oct. in Gore Creevey Papers (1948) 104: To play second fiddle to Brougham [...] would not be worth a dam.
Cardiff & Merthyr Guardian 23 Aug. 4/1: Cobbett found a reformed House of Commons ‘not worth a — ’.
[US] ‘His Nose Sticks Out a Feet’ Jolly Comic Songster 218: Now when I wur but ten years old, I wasn’t worth a darn.
[UK](con. 1840s–50s) H. Mayhew London Labour and London Poor III 80/1: When the telescope was finished, it wasn’t worth a d--.
[US]‘Artemus Ward’ Among the Mormons in Complete Works (1922) 277: ‘Wall,’ the man sed, ‘it’s good for white beans and potatoes, but as regards raisin’ wheat, t’ain’t worth a dam.’.
[US]C.F. Lummis letter 10 Jan. in Byrkit Letters from the Southwest (1989) 241: These measly little streams are not worth a dam.
[UK]Sporting Times 22 Feb. 1/4: Weel, I think it wouldna, be worth a dam——.
[US]N. Davis Northerner 222: Any influence which I might have ordinarily won’t be worth a continental damn to-night.
[US]R.W. Brown ‘Word-List From Western Indiana’ in DN III:viii 584: not worth a damn, by lots of cussin’, adj. phr. Very worthless. ‘Why, his corn’s not worth a damn, by lots of cussin’.’.
[Ire]Joyce ‘Ivy Day at the Committee Room’ Dubliners (1956) 127: Crofton (he’s a decent chap, of course), but he’s not worth a damn as a canvasser.
[US]T. Wolfe Look Homeward, Angel (1930) 190: He ain’t worth a damn until he’s got a quart of corn liquor under his belt.
[US]J. Conroy World to Win 109: I lost my glasses. Ain’t worth a damn without my glasses.
[US]N. Algren Man with the Golden Arm 170: The only thing it [i.e. a drenching with water] ain’t worth a damn on is a woman under sixty or a girl over twelve.
[UK]W. Eyster Far from the Customary Skies 299: Diction-airs ain’t worth a drat [...] People don’t talk those words.
[US]H.S. Thompson letter 29 June Proud Highway (1997) 56: At least no one worth a damn.
[US] ‘The Open Book’ in G. Logsdon Whorehouse Bells Were Ringing (1995) 111: The clap ridden slats in their ten gallon hats / Ain’t worth a damn that I know.
[UK]M. Collins Keepers of Truth 4: Language changes. It ain’t worth a damn.
[UK]V. McDermid Out of Bounds (2017) 100: ‘We never had a single suspect worth a damn’.