This episode is about child abuse, and the mental problems that arise therewith.
Just kidding. This episode is about the day when everyone in the entire world crapped themselves, and the process by which these events were able to take place.
The episode definitely has its moments (for example, the South Park version of Yoko Ono is hilarious). But overall, I thought that this episode was weak. The storyline was a little too much for me. However, some of the episode's other elements were very successful.
For example, seeing Kenny G on South Park was hilarious. And what else would Kenny G do on South Park besides molest someone?