Secret men's business
is a common classless Australian
term meaning just about anything a group of men like to do, without women.
Common examples of secret men's business would be (a) going to the pub, (b) going to the hardware store, (c) going fishing, (d) going to the footy.
The term gained popular currency in the mid 1990's with the media-driven political battle between female aborigines and the white majority. "Secret women's business" is a quite authentic aboriginal term for woman's magic, or that which should not be known by men.