Alright due to the sheer idiocy (lack of imaginable intelligence) in the world, many of the words said today are used in a slang (Insuperior to proper speach) form of communication. Due to this I will be giving you the "Proper" definition for these words.
Purpose: (An Acronym)
Definition: Fornication Under Consent (Command) of the King.
Additional Information: I have also noticed that many people use the word fuck in a variety of ways, usually high schoolers use these words in this context but some of the examples are "Fuck You", "You Fucking Fag" and "MotherFucker"
I will now counter these sayings.
Fuck You? The most logical explanation of this would mean your using the word "Fuck" as an enraging insult or anger towards someone, but if you look closely their is no word besides Damn, which is also used improperly these days that can be used like that. So in honesty you are saying "Fornication Under Command of the King You" which makes no sense whatsoever, and leads to this series of words being illogical.
MotherFucker? Mother Fornication Under Command of the King? Sorry illogical in all aspects, and completely redundant.
In conclusion idiots fill the world these days and you need to learn to stop using slang.
In the old english times Fuck was used to refer towards reproduction under consent of the king, but later during the increase of battles, and the need for larger armies, the king began to command that others reproduce for him, thus Fornication Under (Command) of the King.
This basically means that a woman and man would engage in sexual contentions and reproduce for the kings army, they were then well rewarded and the child was trained. Of course this would take many years and thousands of children to even gain a moderately good army division, in time a large branch of "Elite" soldiers was formed.