A GIF based on documentary footage of then 5-year-old kid Jessica Leonard, who weighed at one point 230lbs. Despite her health difficulties, she still tried to be happy, and was filmed dancing. The resulting video clips went viral on YouTube and as GIFs like this, although many people used the GIFs as a mockery of fat people.
GIF: crazyfatkid DATE: 01/09/2007
Credits: Ratedesi Forums, Cheezburger Know Your Meme