The #HoldACokeWithYourBoobsChallenge went viral in May and for reasons unexplained, hundreds of women thought it was an awareness campaign for breast cancer and jumped on board, posting revealing pictures that demonstrated what gravity could do.

Within days, the women who thought they helping others were told that they had been duped – the stunt was created by US model Gemma Jaxx, who wanted to mock viral charity campaigns.

She wrote on her since-deleted Facebook page: "We were making fun of all these other challenges. We never thought it would take off like it did."

But the fact so many people mistook it for a charity challenge is telling.

Once, charities simply grabbed a colour off the rainbow, sold some ribbons and called it a day. Not anymore. Competition for funds and attention is at an all-time high and charities have to do more than host an afternoon tea to stand out from the crowd.

Some of these unconventional campaigns have been widely successful, including Movember (prostate cancer and male depression), the Ice Bucket Challenge (motor neurone disease) and The Great Shave (leukemia).

But for every mo' a bro grows, there are countless other charities trying to find the right gimmick to hook people in. And some of them are a bit odd.

Apparently, wearing lipstick will raise awareness for MS; wearing high heels will bring more attention to domestic violence; flashing your bra colour will bring awareness to breast cancer and a "smeared lipstick selfie" is what is needed for ovarian cancer.

There is also the endless parade of super-fit runners, swimmers and cyclists who pledge to complete feats of extreme endurance in return for a few charity bucks.

Overseas, the gimmicks are even more extreme. In Japan, men raised money for AIDS research and in return could squeeze a porn actress' breasts. It was called "Boob Aid".

There are more charities than ever competing for the same donation. Since its inception in 2012, the Australian Charities and Not-for-profits Commission registered more than 6000 new charities, bringing the grand total to almost 55,000. There's also an additional 600,000-odd not-for-profit organisations.

And the dollars they're all chasing are getting tight. A NAB index on the industry's grow revealed that charity giving grew by just 2 per cent in the 12 months to February 2015. This is compared to the 10 per cent growth recorded the previous 12 months. Rising unemployment and a jittery economy is forcing many to close their wallets.

David Crosbie, chief executive of the Community Council of Australia, says "stunts" can run the risk of damaging a charity's image or its message getting lost in the hype.

"Unless you've tested that message, and unless that message aligns with the kind of values you're seeking to have people associate you with, it's probably not going to work."

Most "magic bullet" campaigns don't work, he says, because fundraising requires testing and investment in messaging and targeting.

In 2013, Sister2Sister – a group that supports disadvantaged young women – came under fire for its "Step up for the Sisterhood day" which asked participants to "slip into your most glamorous pair of stilettos" to help "stamp out abuse and neglect" for young women at risk.

Daily Life columnist Candice Chung wrote that the well-meaning campaign gravely missed the mark.

"The irony of asking privileged women to put on a nice pair of pumps as an act of solidarity to young women who come from a life of abuse and neglect is pretty hard to stomach," she said. "No one likes a grim marketing message, but turning awareness-raising into an easily digested and 'fun' message risks trivialising the experience of those who are truly in need."

The biggest criticism charities face when asking people to post selfies or play dress-ups for a day is that the message risks getting lost, especially if the campaign is controversial or deemed vain (see selfies, again).

For established players, this new-wave of campaigning has forced them to think outside the box. Oxfam Australia's director of public engagement, Pam Anders, is happy to see the innovation and fresh ideas, but warns that campaigns have to match the charity's message.

"If a gimmick works, it works, but you're only as good as your reputation and the trust people give you by way of money or time, so any idea we have, we have to constantly weigh up risks."

Rob Edwards, chief executive of Fundraising Institute of Australia, says: "It's a pretty crowded market out there and how do you cut through the clutter of all your other competitors to try and see the value in your cause?"

Despite the increasing numbers of charities asking people to shave their hair or not to drink for a month, the most successful way to raise funds is still direct mail, Mr Edwards says.

"At the end of the day, it's about finding a message that resonates with people and is engaging."