In ancient England people could not have sex unless they had consent of the king (unless they were in the Royal Family ). When people wanted to have a baby, they had to get the consent of the king, and the king gave them a placard that they hung on their door > while they were having sex. The placard had
F.U.C.K.
(
Fornication Under Consent of the King
) on it. Hence that's where the word Fuck came from.