Monk then posted the picture on his Facebook page - incurring the wrath of swimming officials just weeks out from the 2012 Olympics in London.
The pair, both not averse to controversy, were ordered to remove the picture, which featured Monk with high powered SWAT-style shotguns and D'Arcy with a pair of handguns.
They were on a camp in California when the picture was taken.
The photo was quickly removed - but not before going viral.
Nick Green, Chef de Mission of the Australian Olympic Team said the picture was foolish and inappropriate.
"SAL’s social media policy has a take down clause," a statement said.
"They have enforced that clause today. Our social media policy also contains a take down clause and we will use that where we see fit during the London Games.
"Anything that is not in the Olympic spirit, or does not follow our guidelines will come down.
"There is no such thing as privacy on social media. Anything that is put up will be in the public domain.
"This incident serves as a warning to all athletes on the 2012 Team about the dangers of social media.
"We say again to our athletes, do not put anything up on social media that you would not share with your mother or your grandmother.
"By all means use social media, but use it responsibly."
Swiming Australia issued a statement indicating their anger.
"Swimming Australia became aware of inappropriate photos posted on athletes' Facebook pages and Twitter accounts this morning," the organisation said in a statement.
"Swimming Australia instantly contacted the athletes involved to ask for them to be removed under Swimming Australia's Social Media Guidelines.
"The photos have been removed.
"Swimming Australia does not condone the posting of inappropriate content on Facebook, Twitter or any social media platform.
"This is a timely reminder for athletes to be more responsible to themselves, the public with whom they engage through social media, and the reputation of the sport."
D'Arcy is still struggling to shake the controversy of his assault on fellow swimmer Michael Cowley which has brought him years of unwanted headlines.
And Monk has also enjoyed a chequered past after lying about breaking his wrist in a skateboarding accident - and then having to admit his deception.