When I was little, my father explained the term as "...all fouled up."
That ain't the word they use in the army, son!
The Clark Gable reference isn't the only anachronism in "City on the Edge of Forever." There's the scene in which Kirk and Edith are walking together and the song "Goodnight Sweetheart" is heard playing on a radio in the window of a radio repair shop. That song was first recorded in 1931.
EDIT: Oh, that's already mentioned on the Memory Alpha page.