Green’s Dictionary of Slang

motherfucker! excl.

also mothahfuggah! sister-fucker!
[motherfucker n.]

(orig. US) a general excl. of surprise, rage etc.

[US]H. Rhodes Chosen Few (1966) 57: They were brought to the sergeant’s attention by the girl yelling ‘MOTHAHFUGGAH!!!!’.
[US]R. Price Blood Brothers ‘For thirty bucks all you get is a hand job, if you wanna get laid it’s an extra twenty.’ [...] ‘Motherfucker!’.
[US](con. 1969–70) D. Bodey F.N.G. (1988) 181: After a few strokes he goes under again and this time lets go of the weapon. Motherfucker! I begin swimming toward him.
[US]D. Hecht Skull Session 124: ‘Motherfucker!’ Paul said, panting.
[UK]Observer 9 Sept. 10: I’ve walked a sister-fucking 20 kilometres already on this motorway, following those sister-fucking signs for the TGV. Sister-fucker!