Before it hit tumblr, Flutterjuice was seen in SorcerusHorserus' Dash Academy Chapter 2, Part 4, posted September 10th, 2011, where Fluttershy is seen in the background with a juicebox in the last panel. SorcerusHorserus was interviewed about her possible role in this meme as well as the tumblr phenomenon, which can be seen here.
There was a now inactive tumblr called Flutterjuice dedicated to posting and reblogging pictures of Fluttershy or other ponies depicted with juice boxes.
- This from AskPosey
- This from Ask Posey
- This from Ask Princess Luna (featuring Trixie)
- This and this from AskStonedTrixie
- This from Ask Surprise
- This from Ask the Flower Trio
- This from Fluffy Ponies