Green’s Dictionary of Slang

1. lit. or fig., a sheep.

1989		R.G. Barrett Boys from Binjiwunyawunya 233: I’ll leave the St Kilda dag rattlers to drink on their own.
2000		F. Ludowyk in Ozwords Oct. 🌐 A dag-rattler, for instance, is a sheep. From this arose the idiom to rattle (one’s) dags, meaning ‘to get a move on’.

2. a male homosexual [the image is of bestiality but the emphasis is on the male anus].

1989

R.G. Barratt ‘Poofs on Parade’ in What Do You Reckon (1997) [ebook] Why these dag rattlers have to blame heterosexuals [i.e. for AIDS], and anybody else that can’t condone their lifestyle [...] is beyond me.

(Aus./N.Z.) to hurry up, to get a move on, esp. as excl.

1968		G. Slatter Pagan Game 161: I’m not overstruck on that new cop. – / Told me to rattle my dags out of there.
1969		B. Mason Awatea (1978) 27: At the double! Rattle your dags!
1971		N. Armfelt Catching Up 48: They call it ‘Twist’ [...] I’d call it, ‘Rattle your dags’!
1982		(con. WWII) E. Sandys Love and War 271: Come on, come on. Rattle your dags.
1998		D.T. Schaller Stalking the Wild Kiwi 🌐 Ch. vii: ‘Rattle your dags,’ Ross would tell us with a grin: hurry up.
2001		Craccum (N.Z.) No. 23 🌐 A person from London might find someone yelling ‘rattle your dags’ a bit strange, and a threat to put a ‘weta in your sweater’ a bit odd, which let’s face it, it is.