This post is largely inspired by this comic about when or if rape jokes are ever acceptable. Go read it, the 30 or so seconds you spend will be well worth it.
Comedy is something I think about a lot at a theoretical level, because I like funny things and I'm a nerd. In college I did improv under the tutelage of the inestimable Dr. Douglas J. Shaw, who in addition to teaching me a lot about the art of making the funny, also really encouraged me to think about why something is funny, why one thing is funnier than another, and why jokes work or don't work on any given level.
And because I'm a nerd who likes to think about these things, and have similarly nerdy friends, I find myself getting into a lot of discussions about how or if certain humor works. These discussions generally center on "edgy" types of humor, like racial humor (not racist humor that attributes motivations to people based on their skin color, but humor that invokes the idea of race).
Racial humor is really tricky because the hory nature of race relations in America creates a context wherein racial jokes are operating at a certain level of understanding regardless of the intent of the creator. When a typical joke fails, it's just simply not funny. But when an attempt at racial humor fails, it ends up not only being not funny, but also tends to sound pretty dang racist, even if that's not the intention of whomever's making the joke. Being a civil libertarian and big fan of free speech, I'm never one to say any particular topic is off limits for jokes, but it's obvious one needs to exercise extra caution when trying to make a racial joke, if for nothing else than not screwing it up and looking like a jackass and/or offending/upsetting folks.
And this obviously extends beyond the example of race into any number of other areas of comedy that deal with things that are potentially offensive or hurtful. Jokes about rape run a very similar razor's edge between possibility of humor and possibility of offense, probably even more so than racial jokes. This is likely compounded by the fact that one can usually tell if someone of a particular racial or ethnic category is around, and most people are then forced to ponder whether their joke is actually funny and worthwhile or if it should just maybe be left unsaid, if not for noble reasons then to at least avoid looking like an asshole.
However, rape is usually an invisible status, in that you're probably unlikely to know someone has experienced rape or sexual assault unless you're a very close friend/family member, and even then, there's a good chance you wouldn't know. And given the somewhat reliable statistics we have on such things, we know roughly 1 in 3 women will experience rape/sexual assault in their lifetime (the numbers we have for men are not nearly as reliable for a number of reasons, but I've seen estimates that put it at about 1 in 10).
So chances are very good that when you make a rape joke, you are doing so in the presence of someone who has been raped. But because this is, again, not usually something someone advertises about themselves, people seem to be more cavalier in making such jokes because they're not forced to take the extra moment to think about what they're going to say, like they probably would be with making a racial joke in a racially diverse group. Teaching criminology courses I often have to talk about rape and sexual assault, but even in a setting where I'm not going to be making any jokes about the subject, I still have to take a lot of care to measure my words. Because again, I know that statistically in my class of 100, there are probably anywhere from 10 to 20 women who have experienced rape or sexual assault, and likely a small handful of men as well. And given that most such assaults occur during the high school and college years, it's likely a very fresh memory for most of these people. I lecture about the subject because it's a necessary component of some courses, but the last thing I want to do is dredge up painful feelings about a horrible experience of my students just because I was cavalier with my language.
Again, the point is not that one can never make a joke that involves rape (as one friend is fond of saying, you can joke about anything as long as the joke is actually funny), but that such a joke requires an extra level of scrutiny before being delivered. Because rape can be (though is not always) an incredibly devastating experience for someone, and when you dredge it up just to make a lame groaner that isn't even funny...well, that's just a pretty shitty thing to do. Rape is really one of those topics where you should only joke about it if you come up with something to funny you simply can't avoid saying it.
So although I understand that for some rape is a subject that should simply be off limits for jokes, I can't quite go that far, because I, too, somewhat share the view that any subject is acceptable if the joke is truly funny enough. But I do absolutely agree with the comic that if you're one of those people who compares the cost of textbooks or the amount of papers you have to write or the taxes you have to pay to rape...well, you're just an asshole.