Those "explanation" of the F-word are what is called folk etymology: Trying to come up with some superficial explanation of a word without looking into the actual history of the word.
If you look into Snopes, you'll find those "explanations" exploded.
POSH (supposedly Port Out Starboard Home) is another popular but false folk etymology.
As a very effective rule of thumb, any time you see a word "explained" by use of an acronym, you can be pretty sure that the explanation is folk etymology. The use of acronyms to make words (such as the historical SNAFU) is modern, just not part of the way the language developed before about the early 20th Century.