Green’s Dictionary of Slang

an excl. of joy, excitement; often ironic.

1788		‘Cherry Cheek Patty’ in Banquet of Thalia 6: I whistle, I whistle, and whoop gee wo Jerry.
1895		S. Crane Red Badge of Courage (1964) 107: ‘Whoop-a-dadee,’ said a man, ‘here we are! Everybody fightin’.’.
1997		C. Hiaasen Lucky You 149: Chub said, ‘Whoop-dee-doo.’ He put the pistol in his belt. ‘Fuck the rock pit.’.
1997–2000		College Sl. Research Project (Cal. State Poly. Uni., Pomona) 🌐 Woopty-woo (interjection) Exclamation when something good has happened.
2005		P. Temple Broken Shore (2007) [ebook] The big boss woman’s supposed to have sacked all the dirtbags [...] but whoopy do, here we go again.