You've seen it many times before: people who act like incredible asshats, and, when confronted with their behaviour, demand they were "only joking" and act as if the target of their venom owes THEM an apology for not laughing along with them.
I've never had much use for such people, and take their defense for what it is: the attempts of angry, venomous people to rationalize their actions by passing incredible nastiness off as some misunderstood joke.
Now, to be sure, there are some people who have a rather acerbic sense of humour. But usually when they make a comment, there's enough wit in their remarks that they are easy to see for what they are...certainly, most people don't get offended by the barbs of comedians, and they can usually understand when a sitcom targets something that hits close to home.
I've raised my children with a certain ethic: if it hurts someone, or hurts their feelings, it is NOT funny. Sure, it's funny to tease, but there's a line you just don't cross. And if you're not a person that can tell where that line is, it is probably best not to go there.
From my perspective, joking also is contingent upon a certain level of familiarity. Jokes around the water cooler, for instance, are funny because these are people who know each other from working together day in and day out. Jokes among family members are also born from a similar level of familiarity. If I were sitting in the Oval Office with the President of the United States, though, there are 1001 jokes that I would NOT tell. And some of them are rather good. Because I don't know the man well enough to make jokes at his expense.
When people pass of general meanness and nastiness as "merely joking", they are in a sense further extending their abusive nature. By demanding that the victim of their joke accept their nastiness as a joke, they effectively deny their victim the right to be angry, no matter how justified their reaction, a demand they have no right to place on the person.
Of course, some times people will honestly be joking and offend. That happens. But usually when that is the case, the offended eventually realizes that the original comment was a joke and sees the humour in it. But there's an entire other class of people that enjoy hurting other people and use the "joking" defense as an attempt to mask an inner meanness and a sadistic nature. And those people don't deserve to be covered by the umbrella of the defense that they are only joking.