And, "for fuck's sake" = "for the sake of fuck". Just as "for Pete's sake" = "for the sake of Pete", or "for goodness' sake" = "for the sake of goodness".
A form of Text-Talk, part of a newly developing dialect whereby the speaker can convey a lengthy or complicated thought by abbreviating phonetically or through the use of substitutive letters, numerals and characters. I.e. Having sexual relations with a female in a shortened sense.
"I'm so going to ftsooh!", "hey man, are you going to ftsooh tonight?"
F: F#&k
T: The
S: S#&t
O: Out
O: Of
H: Her
The word 'flag' as pronounced by people with thick Belfast accents. The term is a perfect encapsulation of the disproportionate and overblown reaction to the removal of the Union Jack (as in 'de fleg') from above City Hall in Belfast. Where previously it had flown for 365 days per year, it is now flown on 17 designated days of the year - in line with many other British cities.
The event caused a portion of the Protestant community ('fleggers') to make international pricks of themselves as they proceeded to wreck the fucking place, claiming it was another erosion of a 'British' identity they perceive to have been under attack since the horrifying spectre of equality reared its head in Northern Ireland.
The word 'fleg' - and indeed 'fleggers' - fittingly describes a section of humanity unconcerned with knowledge, reality or the vagaries of the English language. Like America's tea-baggers they are ruled by instinct, fear and paranoia with a side dish of rampant bigotry and startling ignorance of the world around them.
"Wat de fuck like! The taigs got de fleg took down! Let's wreck de fuckin place! No surrender!"
"De fleg has been took down! Before ye know it there'll be a united Ireland! Attack Short Strand! God Save The Queen!"