First case. Looking through the minutes of a meeting, I read Tom complaining that Jim had been insulting him. Specifically, Jim had been calling Tom a cunt. Jim responded to Tom's complaint as follows: "You are a cunt!"
As I pointed out to Jim, those who study these arcane matters agree that calling a man a cunt is much more insulting than calling him a prick. The insult therefore expresses not just a general contempt for the genitals of both sexes, but an especially intense contempt for female genitals and by implication for women as such.
Jim replied that his insult was not sexist as it had been aimed at a man not a woman. (There were women present, however.) He agreed that it would be wrong to call a woman a cunt. Besides, he and Tom were now friends again. He also observed that this bit should not have been included in the minutes.
Second case. X, a male participant in an e-mail discussion group, circulated a long diatribe against a former comrade, Y, also male, in the course of which he called Y a slut. I objected to this use of "slut" as an insult, because the word in its original meaning expresses contempt for a woman who has sexual relations with multiple partners. Such contempt is again reserved for women, as shown by the fact that there is no equivalent insult for a man who behaves similarly.
X replied that the sense in which he had used the word "slut" bore no relation to the meaning I attributed to the word.
For the sake of fairness, I note that in both cases the response to my criticism was polite. Neither Jim nor X disputed that sexism was something to avoid. However, I saw no sign that either of them had grasped the point I was trying to make. As that point is surely not so very difficult to grasp, I suspect that they were trying NOT to understand. Or is that paranoid?