Green’s Dictionary of Slang

(Aus.) underwear.

1985		R.G. Barrett You Wouldn’t Be Dead for Quids (1989) 190: Why don’t you whip her Reg Grundys off.
1996		S. Maloney Brush-Off (1998) 286: Ken would start to go through my pockets and find what I had in my Reg Grundys.
2002		Pete’s Aussie Sl. Home Page 🌐 Reg Grundy’s (Reggy’s): undies.
2016		N. Cummins Adventures of the Honey Badger [ebook] [W]e had to wear these disposable grundies – or mosquito nets – for the old tackle.
2019		Twitter 2 Nov. 🌐 Nice that Al’s being thrifty and imaginative with his old grundies.