An acronym for "For fuck's sake", meaning "I can't believe this shit, I demand you to stop"
The
source is For Christ's sake ("in Christ's name please explain/stop that"). Swap in
Fuck All ("nothing") for the deity, and you get an urban, angry,
non-religious, expletive, demanding equivalent of "Oh My God, do something".
1. For fuck's sake, where did you get that godawful haircut?
2. FFS, I've explained it to you five times
already.
Now STFU!