The whole point is we're trying to protect people from offensive behavior. The definition of what's offensive is vague at best. Common approach - if someone was offended, it's offensive - assumes that we trust victims accounts that they were in fact offended.
While context is important, it is much harder to believe that someone would be seriously offended by a joke when they make the same kind of a joke themselves. That's why the tweet is relevant.
The only problem with this reasoning is it seems dangerously close to the "they were asking for it" argument. If you are raising concern for something, the entire history of your life does not automatically come into question; this is just an unfortunate side effect of the record-everything technological society we now live in. Corollary to the upcoming ubiquity of Google Goggles, what if the recordings of one's personal home life was scrutinized because they were harassed at work?
And quite often, we find that something that wasn't offensive yesterday can very well be offensive today.
That's a valid concern in general, but I don't think it applies here for the following reasons:
First, being part of a minority group and claiming offense gives you a lot of power to inflict damage on others. You are leveraging both, the legal system and very strong social stigmas. There is a reason why you are granted this power, but with power comes responsibility. If I walk on a sidewalk and bump into someone, I say I'm sorry and we go about our business. If I'm driving a 18-wheel truck and bump into someone, it's an entirely different story. We don't have a magic gauge to measure your emotional state, so we have to take your word for it. I think scrutinizing your past to ensure that what you say is at least consistent with what you do is a reasonable measure to prevent people from abusing the aforesaid power.
Second, if something wasn't offensive to you yesterday, but suddenly is today - even if I'm most sincerely trying to avoid offending you, how do I keep up with the "list of things that offend you" du jour? Do you have a protocol in mind?
That's a slippery slope fallacy, and no, it's not dangerously close to that. If you make a certain kind of joke, I would have a very hard time believing you were offended by that same kind of joke when those two events happened within hours of each others.
As far as I've seen, people's atitudes towards crude jokes do not change in the space of a few hours. Maybe they might change that quickly if something significant were to happen in that space of time, but I doubt it in this case.
There's nothing wrong with the logic of "they were asking for it" in some contexts. Rape, violence, etc. of course not, but I think when it comes to being insulted, saying that someone was asking for it is fair. I've been attacked verbally before, and often I was asking for it or deserving of it.
That said, I don't think this is a case of her asking for it. It's just pointing out hypocrisy, which is a perfectly OK thing to do. It's less extreme but analogous to pointing out someone who complains about domestic violence being themselves an abuser.
The whole point is we're trying to protect people from offensive behavior. The definition of what's offensive is vague at best. Common approach - if someone was offended, it's offensive - assumes that we trust victims accounts that they were in fact offended.
While context is important, it is much harder to believe that someone would be seriously offended by a joke when they make the same kind of a joke themselves. That's why the tweet is relevant.