Green’s Dictionary of Slang

1. (Irish) a term of abuse, a ‘fucker’.

1957		G. Kersh Fowlers End (2001) 29: I’ll burn your effing show down to the effing ground; eff me if I don’t you old effer.
1970		C. Brown Down All the Days 49: You didn’t crack till you had me tied hand and foot with a dozen shitty little effers!
1998		P. Doyle (con. late 1950s) Amaze Your Friends (2019) 248: ‘You never know what these effers have been eating’.

2. (also effer and blinder) a user of obscenity.

1980

Barltrop & Wolveridge Muvver Tongue 94: The effer-and-blinder advised to wash out is mouth.