When in a situation where someone might say something terrible, I'll sometimes go ahead and say it jokingly. The way I see it, getting everyone to laugh at how ridiculous it sounds is way to reinforce that it was unacceptable. And sometimes I think it was there anyway - somebody was thinking it but not saying it or it was implicit in their thinking and they didn't even notice.
For instance, when discussing which interns should be assigned which tasks, John was initially paired with the IT department. Then we realized that John was unavailable that day, so it defaulted to Julie. And I feigned puzzlement for a moment and said "Are you sure we should't wait for John? Girls don't like computers." Which was my way of needling my co-worker about the fact that initially defaulting to the male intern might not have been entirely arbitrary. I knew him well enough that he'd take my point without feeling like I was accusing him.
TL;DR, I think there's a difference between a sexist joke and joking about sexism
And nobody gets to "decide" what everyone else should feel. What I have a problem with is the idea that it's not the meaning of your utterance that makes it offensive, but merely the topic. The idea that tome expressed in the parent comment that there was literally no circumstance under which you could joke about women being treated unfairly (even if it was to call attention to the problem).
I find the idea of someone declaring what's "not okay" for everyone else to be as upsetting as a boor telling a mean-spirited joke and insisting that nobody should be offended because it's just a joke.