Green’s Dictionary of Slang

1. a phr. of excitement or anticipation, usu. about a possible sexual conquest, or when a night out or drinking session is arranged; also as excl.

2003		‘Kissing – So Bros’ Guide’ on BBC.co.uk 🌐 Firstly, be sure you’ve picked the right time, place, girl, etc. All sorted? Game on!
2004		Shystie ‘Unfinished Bizzness’ 🎵 It was game on when I saw him.
2009		Mail & Guardian (Johannesburg) 22 Sept. 🌐 The Indian called Symonds a ‘monkey’. Game on! A massive hate-ball tonked straight up in the air.
2012		G. Flynn Gone Girl 175: [of an incipient emotional clash] We both smiled at each other: I know and you know. Game on. I actually thought those idiotic words: Game on.

2. a phr. of triumph at having sorted out initial arrangements.

1999

Guardian 22 May 🌐 From that moment it’s game on for the crowd as the action whirs in and out and over our heads.