How do you punctuate what FFS expands to?

Question

I was just having a discussion with a friend, and we were wondering about appropriate grammar usage when one says For fucks sake.

In my opinion, there are three candidates:

1. for fucks sake
2. for fuck’s sake
3. for fucks’ sake

My money is on (2), assuming that being a "sake" is possessive.
(3) seems a bit plural and (1) kind of random.

Which one is best, and why?

I’d just like to add, this is not a joke question — I am genuinely interested as to the right way to do it. If you’re going to write out coarse profanity in full, you may as well do it right.

Answer 1

I have always written it as 'for fuck's sake' when I have needed to.

Definition of 'FFS'
in British English
slang
ABBREVIATION FOR the taboo expression 'for fuck's sake': used esp in social media, text messages, etc to indicate irritation

FFS (Collins Dictionary)

Also Lexico and possibly others

I don't know if the unabbreviated FFS counts as a minced oath, exactly, but it seems to be used where more pious ages used for Christ's sake, for Jesus' sake, for God's sake etc. I firmly believe 'fuck' is a noun capable of possession in the exclamation. When I was a schoolboy we had to join the school's section of the Combined Cadet Force and go to drill training once a term at the Grenadier Guards barracks. I distinctly remember a drill-sergeant shouting at me 'What in the name of fook do you fooking think you're fooking doing?' at my attempt at presenting arms.

Answer 2

It probably doesn't make a lot of sense to analyze an interjection according to typical grammatical rules. These sorts of interjections, or exclamations typically are not used as parts of complete sentences.

For example, how would you analyze the exclamation, "whatever", as in:

Person A: You should be more careful.
Person B: Yeah, whatever.

It might be possible to see "whatever" as a highly abbreviated expression of the thought: "Whatever you say, you can't make me care." But realistically, that is not what's going through the speaker's head. It's really not an abbreviation, though historically it may have started out that way.

The most compelling argument (maybe the only compelling argument) for the correct spelling on this interjection would probably be based on the accepted spelling of similar expressions.

For fuck/s/'s/s' sake closely resembles
For God's sake
For Christ's sake

Which would favor "for fuck's sake".

But there's also

For goodness sake

This seems to suggest that "for fucks sake" might be correct, or possibly even "for fuck sake." I know that I, for one, do not pronounce two distinct s's. Perhaps the only s I'm pronouncing is the s in sake.