Green’s Dictionary of Slang

dog n.1

[var. on dad n.1 ; dag n.3 ; dod n.1 ; despite possibility, coinage is too early for backsl.]

[16C; late 19C+] (orig. UK, latterly US) a euph. for God, used in a variety of mild, semi-blasphemous oaths.

In compounds

dog-durned (adj.) (also dog blasted)

[late 19C] (US) a euph. for god-damned adj.

In exclamations

dog bite ’em! (also dog bite me! ear! onions! ...their hides!)

[16C; 20C+] (orig. UK, latterly US) a mild, semi-blasphemous oath.

dog blast you!

[1910s] (US) a mild, semi-blasphemous oath.

dogdamn it!

[1960s] (US) an excl. of surprise, annoyance; a semi-euph. for god-damn it! excl.