In order to make our viral videos as viral as possible (meaning irresistible for people to pass around to each other), we've spent a lot of time analyzing the most successfully viral videos of all time.
We've watched everything from the "The Evolution of Dance," to "David After Dentist." From "Charlie Bit My Finger...Again!" to "Charlie the Unicorn."
We found that the most viral videos share a few common qualities: They are either obnoxious and annoying (see "The Annoying Orange") or bordering on "naughty" in terms of scatological or sexual innuendo. It seems adolescent humor appeals to more than just adolescents.
But these are just my thoughts and observations. I'd love to know what you think makes a great viral video and see some of your favorite examples!