The Harm of Seemingly Harmless Sexist Humor

I had posted this as a comment to a related post, but I think not many people saw it, so I’m re-posting it to cast a wider net, and also because there have been some additional developments.
I need help with the following problem: How does one explain the harmfulness of seemingly harmless sexist humor?
Example: my (otherwise very liberal, progressive) boyfriend had a joke on his facebook profile. The joke went something like this: “A study found that alcohol consumption triggers the release of an estrogen-like hormone. So basically, when a guy drinks, he suddenly finds that he can’t control his emotions, he babbles incoherently, and he can’t drive.”

My boyfriend knew this was playing on stereotypes of women which he admitted he doesn’t believe are actually true, but he still found the joke funny because it was “worded really well” or something. He said that since only his friends have access to his facebook profile, and his friends know he’s not sexist, the joke does no harm. I asked if he would put a joke on his profile that played on stereotypes of a different sociological group, such as a racial group, if it were “worded well.” He said he would, but I’m not sure if he was just trying to hold his argument together. He said he’d take down the joke if it bothered me, but that doesn’t solve the problem of having no problem with a sexist joke so long as it isn’t seen by “the wrong audience” who will “take it seriously.”
Then this morning, my best friend’s boyfriend sent out this gem in a mass email to all our friends:
WARNING: IMMEDIATELY MUTE THE SOUND OF THIS VIDEO as it is accompanied by extremely annoying music.
So, same (or similar, anyway) problem. He doesn’t actually think women are bad drivers, but the whole basis for the supposed humor of the video is that “women can’t drive.” I personally think some (not all) of the clips would be funny if the premise were “look at these PEOPLE who can’t drive,” but instead it’s made clear that the fact that they can’t drive is *because* they’re women. Because the stereotype is that bad driving is innate in women, or something.
(I replied to the email with, “so is that why women’s car insurance is so much lower than men’s?” and he responded with something like, “no, it’s because women can cry to get out of tickets.” I guess he was trying to keep the conversation “humorous.”)
Now again we come to the problem: this guy doesn’t actually believe women are bad drivers, and he only sent this video to friends, who know he’s not sexist. But this *is* sexist. It *is* harmful, no matter who sees/hears it.
So, my friend and I have our work cut out for us, I suppose. I really need help with how to explain why this is not acceptable in a way that won’t make them get defensive, but rather open up a discussion that will allow them to question the motivation for their choices and, hopefully, ultimately understand why sexist humor is harmful no matter who sees it. Any suggestions for framing good arguments/links to good literature on the subject would be appreciated. Thank you in advance!