Green’s Dictionary of Slang

(Aus.) an act of defecation that follows a night of drinking (plus heavily spiced food).

1993		Aus. Word Map 🌐 AGB After Grog Bog. The bog you have the morning after the night before: [toilet flush] Oooooh, that was an ABG if I've ever seen one...
1993		Aus. Word Map 🌐 ‘AGB also known in Melbourne as PGB, post grog bog’.
2014		https://www.reddit.com/r/funny/comments/ 18 Mar. 🌐 An After Grog Bog (ABG) is one of the most underrated things in this world.