Mountain Dew is a real beverage that appears in the Season Sixteen episode, "I Should Have Never Gone Ziplining".
Background[]
In "I Should Have Never Gone Ziplining", Cartman was excessively drinking Mountain Dew, and its variants, in order to cope with the various tour groups. Combined with his stomach contents from his previous night's dinner, this gave him severe flatulence and later, severe diarrhea. The diarrhea later attracted beavers, resulting in the boys having to fight them off.
In "Raising the Bar", it is mentioned that Mountain Dew is one of Honey Boo Boo's favorite drinks.
Variants[]
Double Dew[]
Double Dew
Double Dew has twice the caffeine and sugar of regular Mountain Dew, which resulted in Cartman's diarrhea worsening significantly.
It can also be seen briefly in South Park: The Stick of Truth in the basement when you meet the Bard.
Diet Double Dew[]
Diet Double Dew
Diet Double Dew contains half the caffeine and sugar of Double Dew, making it equivalent to a can of regular Mountain Dew. Cartman, not realizing this, claims that Diet Double Dew does not give him diarrhea.