If 'cunt' is a 'pet code between them', there are some other serious issues I have with his character.
You have yet to explain why it is any of your business. There was a joke I was told years ago that may help you understand.
A bird was up north and when the other birds left for warmer areas down south this bird stayed to enjoy the food with less competition. The weather turned cold and he headed south but by the time he reached Pennsylvania it was too cold to continue, its wings were frozen and he fell to earth. Landing in a barnyard he chided himself for not leaving with the other birds. Too cold to move it sat in the barnyard waiting to die. A cow walked past the bird not seeing it lifted its tail and crapped on the poor bird. Oh the indignities of having to die covered in shit. But the crap was warm and soon thawed its wings and warmed the bird up. It was so happy that it might be able to finish the flight down south that it began to sing.
A cat hearing the chirping left the barn to investigate finding the pile of dung the cat dug through it to find the bird. The cat killed and ate the bird.
The moral of the story is: not everyone that shits on you is your enemy. Not everyone that gets you out of shit is your friend. And if you are warm and happy in a pile of shit keep your mouth shut!
Just because the words used between husband and wife are not the words you choose to use does not make it right or wrong. You are not in that marriage. The fact that you feel you have any say in how he speaks to his wife or how she speaks to him is still not your business. I am sure that when I call my girlfriends filthy slut or cock sucker would offend you as well but it is still none of your business. My wife has no objection to how I speak to her or them, neither do my girlfriends why is it your business? More important, why do you care?
I can understand if the wife complained but you have no evidence of this, or at least you have not provided any. When Mr. Clinton was fooling around on his wife I did not care until he lied about it in a court of law. When Mr. Kennedy fooled around on his wife I did not care either and since it was not a matter for the courts I still don’t care and both husband and wife are dead. Why is it that you have to take issue of what happens between a man and his wife?
P.S.
When Mr. Clinton was being impeached for lying in a court of law, people on the left defended him by saying it was a personal matter, with no relation to his government duties. We on the right were lambasted for peeking into bedrooms and minding other peoples business. I now see the conviction of their beliefs! When it is politically advantageous for them they make up lies to justify bad behavior, and when it is politically advantageous for them they peek into bedrooms, and mind other peoples business with “moral outrage”. Face facts, if that is possible, you have no morals and you are never outraged unless it serves your political goals.
Remember Senator Packwood? Forced out of office because a woman did not like the fact that he kissed her. The moral outrage that some old white guy would force a kiss upon a woman showed how bad republicans were. Years later President Clinton gropes a woman in the oval office and it is a private matter. He has sex with a subordinate, in violation of federal law, and it is a private matter.
Once again they have moral outrage because a man does not speak to his wife in a way they are able to disapprove of. It is not that they really disapprove it is that it is a way of attacking their political enemy. They are not outraged at the act they are outraged because he is a republican and they are not.