After designing an amusing smartphone app that allows users to post images of themselves looking at breasts, two Australians who won money to go to the US to meet technology investors have been heavily criticized.

The organizers of the TechCrunch conference have since apologized after a duo pitched a smartphone app called "Titstare" in front of an audience that included a nine-year-old girl.

The Sydney duo's presentation had the mainly male audience laughing, but angered Twitter users and reignited a debate about sexism in the technology sector. Jethro Batts, 28, and David Boulton, 24, pitched their "tongue in cheek" idea at TechCrunch Disrupt in San Francisco on Sunday after winning money and accommodation for the trip to the US in a similar competition.

The conference, run by tech blog TechCrunch, sees software developers spend 24 hours coding a new product and then pitching it before an audience of developers and investors.

In their pitch of Titstare, Boulton said on stage in front of an audience of hundreds (and thousands online) that it would allow users to "take photos of yourself, looking at tits"."It's science my good friend, science," he said. co-founder Batts added : "Did you know male life expectancy decreased three per cent in the last five years?"

Both app ideas resulted in almost universal condemnation online."Titstare guys got a very loud applause from audience. Thank god sexism isn't alive and well in the tech sector. SO PROUD TO HAVE MY KID HERE," wrote Kim Jordan on Twitter sarcastically, the mother of the nine-year-old programmer Alexandra Jordan, who pitched a start-up app idea at the conference called Super Fun Kid Time which allows for the scheduling of children's play dates.

"'Just kidding' isn't a magic responsibility absolving spell," wrote another Twitter user, @jacobian. "You did something really sexist, apologise and own the mistake."

TechCrunch issued a full apology concerning the two pitches on its website.

The Sydney duo's previous idea, which helped get them to the US, was for an app called Hate You Cards. It took out top honors in May at a similar 24-hour coding competition called AngelHack Sydney.

Hate You Cards, which allows users to take photos of themselves and turn them into mean joke text messages and emails to send to their friends, attracted similar criticism, but not to the same level as Titstare.

In the face of ensuing outrage app developer Jethro Batts said the reaction received online was "not what we expected". He said he was not aware children were in the audience and that had he known, he wouldn't have gone ahead with the "tongue-in-cheek" app pitch.

"For anybody out there who was offended by it we're very, very sorry. It was based around a couple of ideas and having a bit of a laugh," Batts said."If we offended anybody it was unintentionally done. It wasn't what we were hoping to do."

Batts added that the presentation was well received by conference audience members and that it had been "misconstrued" on Twitter.

"You have one person who tweets to 50,000 or 100,000 people and if you have that many followers it can get misconstrued," he said, adding that he wasn't looking to make money from the idea.