Faygo is a soft drink available on Alternia. The drink is a noted favourite of Gamzee Makara, who consumes it as part of his cult's rituals, referred to as "kicking the wicked elixir". Through a fetch modus mishap, a bottle is accidentally launched far across the ocean, washing up on Eridan Ampora's island hive, much to his disgust.
Later, while in the midst of emotional theatrics, Eridan is advised by Gamzee to kick back and get his zone on with a cold bottle of Faygo. He indulges Gamzee, and his reaction to the taste of the sugary swill is indifferent.
In human society, Faygo is a sugary soft drink manufactured in Detroit, Michigan and made popular outside its distribution area by the musical group Insane Clown Posse, and a staple of juggalo subculture, on which Gamzee is based. In the post-Scratch universe, the Posse became Presidents of the United States thanks to the manipulations of The Condesce, and one of their actions in office was to replace all tap water with Faygo. Not surprisingly, this made type 2 diabetes so common that having it was considered the national pastime.
After Terezi forms a kismesissitude with Gamzee she also begins drinking Faygo, which she quickly becomes addicted to. She regards it with as much negativity as Eridan does.