The story
From a badly translated Chinese bootleg copy of Star Wars III: Revenge of the Sith titled Star War The Third Gathers: The Backstroke of the West. The original cry "Noooooooo" was translated into Chinese as 不要 (bùyào, “not want”), and then back into the English subtitles as "do not want".
Etymology from Wiktionary, CC BY-SA 4.0.