Great Destinations (a.k.a. The Most Notorious Episode)
In this special Matt & Trey stood in front of a waterfall and introduced "Cartman's Mom is a Dirty Slut" and "Cartman's Mom is Still a Dirty Slut" as being named by Comedy Central as the most "notorious" episodes of the series. Before part 2 began airing in the second half of this one hour event, they relate the story of their April Fool's joke of 1998, which didn't go over very well with the viewers, who took the need to know who Cartman's father was much too seriously.
