Green’s Dictionary of Slang

(Aus.) exciting, pleasurable.

1940		Canberra Times 26 Oct. 3/5: Tickets may be obtained by ringing the Secretary, Phone Queanbeyan 321. A WHACKO NIGHT FOR ALL.
1951		Cusack & James Come in Spinner (1960) 148: We’ll see you have a whacko time at Grace’s party for all you’ve done.
1966		P. White Solid Mandala (1976) 180: What, and breed together? That would be whacko!
1973		L. Oakes Whitlam PM 38: In Margaret’s words, quoted in Women’s Day in July 1972: ‘We’d have a whacko time anywhere – whether at the Australia Hotel or the Cafe de Fairfax to have meat pies.’ [AND].