Green’s Dictionary of Slang

1. in poor taste, socially unacceptable.

1990

R. Doyle Snapper 145: That’s offside, said Jimmy Sr. It was true though.

2. antagonistic; as offside with/from, out of favour, in bad odour with.

1953		B. Behan Scarperer (1966) 36: Breaking out of here is a puddin’ compared to getting offside from the Scarperer, if you try to work a stroke on him.
1968		G. Slatter Pagan Game (1969) 124: Any more of you getting offside with the music master and I’ll cane you myself.
1999		P. Temple Black Tide (2012) [ebook] The question you want to ask, Tony, is this: am I better off square with the Armits and onside with Bren, or one-sixty deep and offside with Bren?
2000		R.G. Barrett Leaving Bondi (2013) [ebook] ‘So besides being one step in front of the gendarmes, Knox had quite a few people offside’.
2003		McGill Reed Dict. of N.Z. Sl. 146: offside 1. In someone’s bad books, often in phrase get offside with.
2018		C. Hammer Scrublands [ebook] ‘What did you do?To get everyone so offside?’.
2020		D. Whish-Wilson Shore Leave 58: ‘You trying to get Cassidy offside?’.