So, I think that rape brings up some pretty unusual feelings and behaviors.
For a while, I was in a relationship with a girl who had been raped by a friend several years before.
What happened next was: essentially all of her friends told her there must have been a misunderstanding and her college threatened her with libel for accusing the guy of rape.
Of course, this girl had one of the darkest senses of humor of anyone I've ever known, and wouldn't have batted an eye at the comic in question. I didn't find it particularly offensive either.
But it's worth thinking about why jokes about rape can be particularly difficult for rape victims. The thing is, unlike crimes like robbery or murder, victims of rape very rarely find that society is "on their side." For one thing, rapists hardly ever are held criminally responsible for their actions--this is not necessarily because we are a pro-rape society, it's just that it's essentially impossible to prove that you didn't consent to sex. And that's true outside of the criminal justice system, too--many rape victims find that even close friends and family cannot know whether a rape occurred, and choose to believe that it didn't. So the rape is compounded by the abandonment that comes afterwards.
Then you have the fact that our culture, and perhaps our genetic nature, glorifies aggressive men, men who understand that women want it no matter what they say. And on the other side, we have the fact that our culture, and perhaps our genetic nature, encourages women to engage in "token resistance"--saying no when they mean yes--to avoid the appearance of "being a slut."
I honestly do not know if this situation can be improved much. Being raped is tough because you can't prove it happened--well, I don't think the answer is to weaken the presumption of innocence. Rape is more likely because we glorify aggressive men--well, I don't think those traits are going away anytime soon.
But to victims of rape, when people call rape "literally the worst possible thing," it can't help but feel hollow. Because everyone says that, it's like a cultural tic, but when you were raped, no one came running to help you, no one believed you, no one even stayed your friend. They explained it away, they left, they told you that you were just guilty about cheating on your boyfriend.
There's this painful, terrifying juxtaposition of a society that says both: "rape is the worst thing ever" and "you were raped? well, goodbye." That might explain the reactions to what, in isolation, is a pretty innocuous joke.