It is an acronym from the middle ages
Consent of the
You would see that on a sign on a door which meant do not disturb because they were trying to make a baby.
People eventually just shorten it to F.U.C.K.
1. An abbreviation, F.U.C.K, Meaning: "Fertility Under
Consent of King."
1) Fuck- In the older times, a couple who wanted sexual intercourse would have to seek audiance with the King. The King would then sign a document, code named, "F.U.C.K" With his approval if the couple were allowed to have children or not.