1941, U.S. military slang, acronym for situation normal, all fucked up, "an expression conveying the common soldier's laconic acceptance of the disorder of war and the ineptitude of his superiors" ["Oxford English Dictionary"]. As an adjective from 1942. In public explanations the word typically was euphemised to fouled.
: It's a very snafu set-up here
: He gave it a good shot, but snafued horribly
[WWII armed forces; fr situation normal, all fucked up]