Green’s Dictionary of Slang

(US) second-rate, insignificant, trivial.

1970		M. Thomas Total Beast 82: That’s all nit-shit stuff, see.
1979		‘Iceberg Slim’ Airtight Willie and Me 41: I’ll spring for the nitshit refreshments.
1987		J. Dickey Alnilam 483: The field is due west of the dam, and it won’t be a whole lot of trouble to line up on the nit-shit runway.
2003		L. McCall Hard, Fast and Slippery 21: You hustle over there and hold his hand. But don’t bring back any nit-shit case.