Green’s Dictionary of Slang

eff n.

1. a euph. for fucker n. (3)

1938

T. Burns ‘Street Corner’ New Writing 73: ‘Saucy effs,’ said the tall girl.... ‘Oo, yer bitch,’ shouted Frankie....

2. (also f) a euph. for fuck n. in various uses.

1961		H. Ellison ‘High Dice’ Gentleman Junkie 93: Who the eff you think you are?
1962		A. La Guma Walk in the Night (1968) 68: You don’t have to worry niks, Mikey. We okay. We don’t give an eff for the law.
1970		A. Sillitoe Start in Life (1979) 84: I was more determined then not to give in, and they could do eff-all about it.
1997		G.V. Higgins Change of Gravity [ebook] He used a lot of profanity [...] Marie and the other wives’re dropping a few effs of their own every now and then.
2000		T. Udo Vatican Bloodbath 146: What the f.!
2000		F. Kellerman Stalker (2001) 230: What the eff happened to your wheels?
2011		Guardian CIF 8 Aug. 🌐 Tell him who the eff I is.

In derivatives

effery (n.)

(Aus.) used as intensifier.

1989

B. Reed ‘Messman on C.E.’s Altar’ in Passing Strange (2015) 23: ’So who the effery care about you’.

In phrases