Green’s Dictionary of Slang

(Aus.) to depart, to go away.

1975		Canberra Times (ACT) 7 June 4/6: [advert] RACK OFF! FOR THE LONG WEEKEND to ‘Normie’ country with the fun people for three days of wining, dining, and high living in the beautiful Hunter River Valley.
1986		C. Bowles G’DAY 7: MACKA: Wossa matter? Dip out? SHANE: Yeah. Put the ard word onner an she told me ter rack off.
1998		P. Doyle (con. late 1950s) Amaze Your Friends (2019) 109: ‘Rack off. I’ll defend myself’.
2016		Facebook 15 July 🌐 Well this morning I got up had a rubbedy dub, a dad and Dave then racked off to the watering hole for a dogs eye with dead horse.