English language linguists agree that the word motherfucker has become so mainstream that it’s no longer considered an insult. But a little history first …
We cannot be sure that motherfucker, borne of fuck was not actually attested in speech by the dates we have first written attestation, and sadly enough they’re the only products amenable to historical investigation. First citations given for the earliest known definition, a despicable or contemptible person date back to 1918:
1918 Letter in Journal of American History LXXXI 1585: Your low-down Mother Fuckers can put a gun in our hands but who is able to take it out? [1918 in H. De Witt Bawdy Barrack-Room Ballads: The little red run he grew and grew/fucked his mother and sister too.] 1928 C. McKay Banjo 229: I’ve been made a fool of by many a skirt, but its the first time a mother-plugger done got me like this.
The word motherfucker then really took off in the Army in World Wars, giving the second sense, a fellow; a person; an admire person; a formidable person:
1958 Stack a Lee (typescript, Kinsey Institute) 1: He…said who put the hole in this motherfucker’s head/Who could the murderer of this poor man 1964 R.D Abrahams Deep down in Jungle (Appendix II) 261: One of the best things which can be said of a man is that he is a “mean motherfucker” or a “tough motherfucker”, but to call him just a “mother-fucker” is to invite reprisal.
Earlier than the above we have of course Austrian born, Sigmund Freud who in his 1909 paper “Analyse der Phobie eines fünfjährigen Knaben“, scientifically concluded that, “We’re all motherfuckers“.
So not only is motherfucker extremely dated, but its significance and impact as an insult has been considerably marginalized by Freud, long before it became part of the vocabulary of these troops. On a further note, Freud was probably also the inventor of the MILF genre [citations needed].
It isn’t hard to see why a motherfucker, someone who fucks mothers, could have easily become a byword of opprobrium and contempt in the past. To have a potential motherfucker walking about, was to have an existential insult that threatens a man’s very identity as a legitimate member of his household.
Fast-Forward to 2014. Internet Porn has changed how people behave inside the bedroom and couples are no longer satisfied with dirty talk alone. Instead they actually live them out in the nearest swinger clubs. And so for those who are living in an open relationship, motherfucker even became a form of flattery. As you can imagine this ambiguity leads to confusion within the club visitors, as one can never be sure if the offer was to double-team someone’s wife or engage in a fight.
Further reasoning along the same lines shows why fatherfucker, which until previously nonsensical, is becoming a more appropriate way of slander as it depicts one of the few taboos left: Incest!
That said, care should be taken never to use the word fatherfucker as an insult to gay man unless you’re a gay man yourself, in which case it’s perfectly fine.
Some linguists argue fatherfucker too is not ideal as it has already penetrated mainstream English. But as a rule of thumb, you should be able to use it at least until films like Pulp-Fiction are remade with:
“‘Look, just ’cause I wouldn’t give no man a foot massage don’t make it right for Marsellus to throw Antoine into a glass fatherfucking house, fucking up the way the African-American talks. That shit ain’t right. Fatherfucker do that shit to me, he better paralyze my ass because I’d kill the fatherfucker. Know what I’m saying?.’”