Green’s Dictionary of Slang

(US) a joc. reverse of motherfucker n.

1965		oral testimony in Lighter HDAS I.
1972		R.A. Wilson Playboy’s Book of Forbidden Words 171: Motherfucker. [...] various timid, euphemistic or quasi-humorous variations such as [...] futher-mucker.
2002		‘Whinge’ 2 Dec. at BansheeWerks.com 🌐 Jesus Christ, music is a moving futhermucker. Plus, I really need some sleep.