Green’s Dictionary of Slang

a euph. for damn n.

1872		Schele De Vere Americanisms 595: The honest damn is rarely heard, it is true, but, ‘fearful of committing an open profanity, yet nibbling slyly at the sin,’ men indulge in countless hypocritical evasions. Darn, durn, and dang, all but thinly disguised damns, appear far more vulgar than the open oath.
1891		W.P. Dempsey [perf.] ‘The bank that broke the man at Monte Carlo’ 🎵 You can hear me slang / With the most outrageous ‘cuss’ and ‘dang’.
1906		Somerville & Ross Some Irish Yesterdays 113: He wouldn’t give a dang for them.
1987		‘Joe Bob Briggs’ Joe Bob Goes to the Drive-In 41: Basket Case was the only thing at the Cannes Film Festival worth a dang.
2002		‘Touré’ Portable Promised Land (ms.) 156: We Words (My Favorite Things) [...] Thang. Dang. Ain’t. Cain’t. Tain’t.