People have a lot of pet peeves. For instance, I don't think it's cool for people who text in the middle of theatre performances, or when you're being asked to pay for someone else's meal when they know that you're broke and you can only afford so much, or when you lend out books and they never come back to you. It's also right up there with people who blow cigarette smoke in your face or pressure you into drinking alcohol because they have no concept of personal boundaries, or not turning off the light when they know perfectly well you want to sleep.
One of my major pet peeves is when people tell you "That was a joke. Don't you have a sense of humor?" when saying something offensive or un-PC or generally being total dickheads. My ex-boyfriend did that a lot to me, to the point where I actually though, at the back of my mind, that I must be one of the ultra-sensitive people in the world because, gosh darn it, why didn't I find it funny that Hitler massacred all the Jews, or that 9/11 was hilarious because of all those dead Americans?
An addendum to this is when people say something deliberately offensive, like referring to girls as "skanks" or saying "You should get a cute, virgin girlfriend" (thereby implying that women who have had sexual relations before are immediately undesirable because of this unnecessary pressure of men on women to remain "chaste" and "pure") and then are offended when other people call them out on it.
It's gotten to the point where there's a part of me that DOESN'T want to call people out on it because I don't want to deal with the fallout, which is more problematic (or perhaps because I do over-think things sometimes). Because there's funny without being offensive, and there's offensive or self-centered or selfish hidden under the guise of funny. I mean, cracking a dirty joke now and then or finding stuff hilarious is great, but when somebody uses the "That was a joke" defense to mask their offensive behavior is basically asking you, the audience/the listener/the friend to whom the statement was directed at, to assume responsibility for what was being said. And it's an unnecessary and unfair responsibility because as the speaker, you are responsible for the words that are coming out of your mouth.
I've always thought of humor as a way of looking at the world, of finding the absurd in a situation that is rife with uncertainty. Certainly, it's a defense mechanism: I would rather find the funny side of things than to wallow in misery and sadness. It's a way of making other people feel more comfortable, to include people in what might otherwise be an uncomfortable social setting, and it's one of those things that, if wielded correctly, will enhance any kind of social experience.
But I never thought it's funny to make fun of serious historical or tragic events. Neither is it funny to use gender stereotypes and insults against other people, because there are a lot of people out there who are facing life-or-death issues that stem directly from this "joke". It's not funny when you're being irresponsible with your words and actions and then making someone else assume the burden of responsibility simply because you forgot to install the filter between your mind and your mouth.
Furthermore, you, the speaker, do not have a right to act offended when someone calls you out on it, or when someone tells you, "Hey that was wrong, you shouldn't do that." (I've noticed guys get reverse-offended this more than girls.) You are in a position of privilege, and I'm pretty sure you wouldn't find it funny if the situation was reversed. No, you do not get to act offended because nobody found you funny - there's a reason for that. And it's not because they don't have a sense of humor.