Why did it go viral?
1-The early versions of the video have a lot of NAKED college kids (We subconsciously pay more attention to naked people unless they are offensive, disgusting or immoral)
2- Just like many other viral videos, the video is about a group of people dancing to the same music in a different way.
3-It is about surprising the viewers by using CREATIVITY. It builds up expectation during the fist half. Even though the first half is boring people still watch it because it is not long and it makes the second half more enjoyable (e.g. from super slow to super fast)