In the world of obscenities, “motherfucker” is a winner. It combines the incest taboo with English’s most vulgar term for the sex act. Interjections typically weigh in light, but this one’s articulation gives you room to play. It’s a long word. Four syllables with pleasing assonances between the first and the third and second and fourth. There is also an orthographic symmetry in the way both halves end in “er”, which transforms into a delightful asymmetry when you realize that “er” is a bound nominalization suffix in the latter case but just part of “mother” in the former. The citation form puts the stress on the first syllable—/‘mʌ ðɹ fʌk ɹ/—but in contexts where the point is to emphasize the element of surprise it may be shifted penultimately.
–So he was Kaiser Soze all along. /mʌ ðɹ ‘fʌk ɹ/!
The common interpretation of “motherfucker” is that it’s your own mother who you are fucking. But why? If you were to just fuck one mother randomly in the world, the chances that you would commit incest are vanishingly small. Conversely, for every mother there necessarily exists a motherfucker, though they more commonly go by the name of “father”. The semantic charm of English’s strongest four-syllable obscenity lies not just in its capacity to offend but also in its literal unlikelihood.
This is a Gricean effect, right? My money would be on the Maxim of Quantity. I wouldn’t have gone to the trouble of using taboo language unless I had meant it to be really taboo, so you should give the maximally shocking interpretation to the “mother” morpheme. But then the quantity in question is not in the world but is rather the quantity of offensiveness in an expression. Is this a meta-linguistic stretch? Canonically we have just four maxims to flout—Quality, Quantity, Relation, and Manner—but maybe the discretization into finite categories is unjustified, and really there’s only one maxim: expect the unexpected.