Green’s Dictionary of Slang

an excl. of irritation or disbelief.

2014		C. Eble (ed.) UNC-CH Campus Sl. Spring 2014 5: F.F.S. — <for fuck’s sake expression of anger or frustration: ‘F.f.s., make your definitions more concise.’ Usually written online instead of spoken.
2023		D. Garner The Upstairs Delicatessen 43: [Laurie] Colwin’s coffee habits make me shudder, though [...] FFS, Laurie. Well, we all have our kinks.