"do not want" does NOT come from 4chan, although 4chan certainly abused the hell out of the phrase.
It is a line from one of the recent Star Wars movies (episode 3 I think) with a boot-legged double translation (ie the audio is English, but there are subtitles that were translated into Chinese and then back into English - obviously the translation was very poor). There are tons of little gem phrases like "DO NOT WANT" when someone is screaming and about to die. The most awesome occurrence was when Vader yelled his famous line, "NOOOOOOOOOOO" and it got translated as "DO NOT WANT." I highly recommend that you watch it if you get the chance, the movie is much better with the strange subtitles.
I don't know if "epic fail" really came from anywhere in particular.