Green’s Dictionary of Slang

a general excl. of annoyance or distaste.

1966		(con. 1958) R. Farina Been Down So Long (1972) 24: Oh ratshit, someone coming over, looks official.
1979		(con. 1949) J. Hurling Boomers 67: ‘Ratshit!’ he muttered.
1982		W. Wharton Midnight Clear 115: Rat’s claws, Shutzer! It’s just not that important.
1989		P. Benchley Lush 90: ‘Ratshit,’ said Crosby. ‘I can’t hit dick left-handed.’.