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
when you're holding up your phone and making faces at it, as though you are taking a selfie, but you're really taking a picture of the person across from you or the wall or anything else that seems interesting but you don't want to be caught dead taking a picture of.
This action is often made more convincing by wiggling the eyebrows or opening the mouth, to pretend you're trying to get a Snapchat filter to work.
FRIEND A: "Did you just take a stealthie of me?"
FRIEND B (turning phone around): "no I was just using snapchat's new filter, see?"