Green’s Dictionary of Slang

(UK juv.) excellent, first-rate, wonderful.

1950		A. Buckeridge Jennings Goes To School 37: What a smash-on bashing-up it’s going to be! Rare! Super-duper!
1958		Kerouac letter 19 June in Charters II (1999) 134: Burroughs, you know, is a superduper Rimbaud-type Raymond Chandler.
1961		(con. 1942) D. Behan Teems of Times and Happy Returns 225: No, wouldn’t do no good, the Vat has a super-duper lightnin’-conductor.
1977		H. Ellison ‘Jeffty Is Five’ in Shatterday (1982) 41: ‘Super duper,’ he said.
1985		O. Hawkins Chili 15: We have just smoked three joints [...] eaten a five pound pot of chili con carne, two pork chops each and a couple other things [...] Easily a case of the superduper munchies.
1999		Indep. on Sun. 27 June 9: He was convincing as a super-dooper head teacher, the Red Adair of morning assemblies.
1999		K. Sampson Powder 90: ‘Everything OK?’ ‘Super-duper,’ smiled Ticky.
2021		‘Aidan Truhen’ Seven Demons 97: ‘[Y]ou are going to be super-duper frank with me’.