What if the joke were "Why did the chicken cross the road? To get to the other side!" and she said that jokes about chickens made her uncomfortable. Is he obliged to stop telling dumb chicken jokes?
I see this case as two people and two companies who acted like children and both lost their jobs and look bad in the community, respectively. Some unfunny man made a joke to his co-worker because he thought it might have eased the social tension that comes from traveling, lodging, and attending a conference with another person over so many hours. An overzealous woman took offense to an overhead comment and saw it more constructive to bring attention to the public conversation that happens on twitter rather than the public conversation happening in that room because it was a more comfortable way to make sense of how she felt.
We're humans and we naturally want to surround ourselves with people who think, act, joke, argue with, and support other people like we do. It's pretty easy to never have to deal with groups we don't agree with on the internet. It's the reason swarms of misogynists got together on the internet to hate Adria and say she represented all the other women that they hate, and to call her awful names and issue a DDOS attack against her parent company.
Both of these companies looked past the human error in all of this, and enforced their zero-tolerance policies, and just fired both of them. This whole thing is a big deal because the other people we align ourselves with and allow to represent us (be it as employees, or pythonistas, or dirtbag misogynists) are making it really hard to connect on personal levels, and really easy to generalize and dehumanize issues into meaningless black or white distinctions.
If someone finds my breathing offensive, am I an asshole if I keep breathing?
I'm specifically ignoring the action of the companies, the firings and all that, because honestly, while I haven't heard the specific joke in question, it really doesn't sound offensive to me, and it seems as though Adria just decided to be offended by it, and while I'm wary of making assumptions (and even mr hank himself seems apologetic), I can't help but be thankful that it wasn't something I said. I was at PyCon, had conversations, and might have even made a joke or two. I don't think I said anything that might have come off offensive to anybody, but given how innocuous this whole thing seems to me, as somebody who admittedly hasn't followed the story, I just can't help but feel some great travesty happened.
When I do offend people, I often like to probe as to _why_ they're offended. In my experience, most people seem to be incapable of defining any concrete reasons as to why a given statement is offensive other than circular, "it's offensive because it's offensive" reasoning.
I think if someone said "Could you stop using words containing "e"? Such words hurt my brain." I think I would.
If someone said "Quit your "e" words, you bad guy!" I'd be less inclined to. "Words with the letter "e" are bad words, and you need to stop using them" even less (the difference between these two being hypocrisy).
Either way, I find it highly unlikely that I would even try to craft e-less sentences, regardless of how offensive someone might find it.
I imagine you're capable of understanding why they might find it offensive and acting accordingly depending on the context, which is the real issue. Whether YOU find it offensive is just beside the point, as it's a given that a person doesn't stand around saying or doing things that they find offensive. Whether you're capable of evaluating the other person's point of view is the key. (I bet you probably are)
If you can see why they'd find it offensive and continue doing it, you're pretty much by definition being an asshole. That's not a moral judgment, I think it's just descriptive...