One generally accepted valid approach towards producing a video ad that will go viral online is to approach a person that has already achieved a reputation on YouTube for their quirky, interesting, sexy, or otherwise attractive videos and use them in the video ad.
We have such an online video celebrity right here in Australia: Natalie Tran and her communitychannel on YouTube which has more than 150,000 subscribers. Her videos have amassed more than 64MM views according to WAToday - that's even more than AC/DC who have 53MM views. Her highest scoring video has more than 11MM views!
Here's your challenge: I am expecting to see at least one viral video campaign come out of Australia with her as the star. Do it right, and you're bound to have a tremendous viral success.