Green’s Dictionary of Slang

1. (US) excrement, usu. fig.; often constr. with sour.

1862		S. Sturgis in Hennessy Return to Bull Run (1999) 92: I don’t care for John Pope one pinch of owl dung.
1948		(con. 1944) N. Mailer Naked and Dead 96: ‘What’s this stuff [i.e. food]?’ ‘It’s owl shit.’.
1972		D. Jenkins Semi-Tough 147: I remember I said, ‘Owl shit.’ Or something.
1987		(con. 1967) Bunch & Cole Reckoning for Kings (1989) 32: Wonder if he knows tanks don’t float worth sour owl shit? [Ibid.] 381: The sights on these gook guns ain’t worth sour owl shit.
1992		D.L. Ouren Pope County Trib. 21 Sept. 🌐 A man often dismissed in popular Civil War histories (including the recent PBS series) as a swaggering braggart, a man ‘not worth a pinch of owl dung’.

2. in fig. use, anything distasteful.

1972

R.A. Wilson Playboy’s Book of Forbidden Words 185: Owlshit. Anything tedious or distressing.