The Origin of the Term:

Several years ago a political event occurred in South Australia.  A new bridge and development of a marina were planned from the banks of the Murray River to an island. ( Hindmarsh Island.)

Various groups were opposed to this bridge and marina.  Attempts by lobby groups to stop it were defeated in the lower courts but they then pulled a bizarre trick. They enlisted a small group of aboriginal women who claimed the site was culturally sacred to them and therefore could not be touched.  Politicians, lobbyists and  bandwagon jumpers took up their cause with gusto but when the courts asked what it was that made this area significant no one actually knew!

Someone came up with a statement that it was "Secret Women's Business"  which could not be divulged to any male (strangely enough it would not be divulged to female lawyers either!) and, believe it or not, this case actually got all the way to Australian High Court without the nature of the cutural significance ever being divulged. Eventually it was revealed the whole Secret Womens Business was a fabrication and at least one gullible federal  politician's career was cut short. The bridge was allowed to go ahead but as a result of the delays and increased costs the original company went broke. The opposers of the bridge got their victory.

The term "Secret Women's Business" has entered  Australian vernacular as an excuse not to divulge something when you have no actual valid reason but just don't want to.

How did we get "Secret Men's Business"?

The above events happened not long before one of our trips and "Secret Women's Business" was already commonly used in conversation. 

We were at the Aero Club having a few drinks and discussing our next trip.  Our trips are boy's only affairs and Sally, one of the female instructors, asked what we were planning.  One of the boys quickly responded " We can't tell you it's Secret Men's Business. If we tell you we'd have to kill you!"

Not long after that  a photo of the group appeared on the club noticeboard  with the hand written name "Secret Men's Business" written across it. The writing looked suspiciously like Sally's and  the name was born!

However  we really didn't formally use it till our recent 2002 trip.