Whether they know why or not, if you make them dance, you are half way there.
The video below is of one solitary guy dancing at an outdoor concert, obviously being filmed because his dancing was far from ordinary. By the end of the 3 minute video the awkward dancer has caused a full on riot of viral dancing. It is truly amazing to watch, and as others have said, a great metaphor of social media and viral marketing.
The lesson? Be remarkable and passionate about what you do. If it is genuine, others will watch, some will join in, and the movement will grow.