Green’s Dictionary of Slang

(US) a general excl. of surprise, amazement.

1961		G.L. Coon Meanwhile, Back at the Front (1962) 10: I’ll be dipped in shit. I’ll be the only man in history got a Purple Heart on the way to a whorehouse.
1977		(con. 1969) M. Herr Dispatches 40: Leaving him with [...] helpless amazement on his face, ‘Well I’ll be dipped in shit!’.
1982		(con. 1970) J.M. Del Vecchio 13th Valley (1983) 159: ‘Well I’ll be dipped in shit,’ Garbageman said.
1989		(con. 1969) W.E. Merritt Where the Rivers Ran Backward 271: Well, I’ll be dipped in shit.