Green’s Dictionary of Slang

nothing, zero; thus as adj., piffling.

1934		Z.N. Hurston Jonah’s Gourd Vine (1995) 116: She ain’t never had nothin’ – not eben doodly-squat.
1958		R. Frede Entry E (1961) 62: I hate this doodly squat betting.
1958		Hughes & Bontemps Book of Negro Folklore 483: doodley-squat : Not caring. I don’t give a doodley-squat.
1961		(con. 1945) G. Forbes Goodbye to Some (1963) 277: The answer is that until now you haven’t lost doodley squat.
1965		H. Rhodes Chosen Few (1966) 31: Blood remembered hearing Blue say more than once that to burn a stranger didn’t mean doodley squat, but to burn a friend was unforgiveable.
1978		S. King Stand (1990) 1263: Nothing. Doodley-squat. El-zilcho. I don’t hear nothing.
1979		E. Torres After Hours 214: You can’t do doodley-squat.
1980		J.L. Gwaltney Drylongso 220: The whitefolks didn’ know doodleesqua’ about it.
1983		S. King Christine 492: A dull thud of pain rumbled up my left leg, the one that still wasn’t worth doodly-squat.
1984		I. Doig Eng. Creek 247: He don’t see doodly-squat about putting up hay, that fellow.
1993		R. Shell Iced 199: Without a will, that man will do doody-squat! Neeesch!