Don't ask me about that limerick. Just don't. Please. (source)
Obviously this is a pretty extreme (and comedic) example. But in our modern world of text messaging and internet forums, it's pretty easy for a joke to get out of hand. Sarcasm is much more difficult to understand via text, when you don't have things like facial expressions and body language to help people along. I've seen numerous internet discussions get way out of hand because someone made a joke that someone else took out of context. The people who make the joke, of course, always blame the other person, saying that they were "just joking" and how on earth could anyone possibly miss that? Yet plenty of intelligent adults miss jokes all the time.
The other day, my mom sent me an e-mail full of pictures. Each picture represented something else, and you had to guess the word that it meant. For example, a picture of an alligator standing over a gurney was supposed to represent the word "gatorade." As in "gator" and "aid." Yet I never would have gotten that. Why? Because when I see a gurney, the word "aid" is not even in my brain. I'm thinking about the word "gurney."
There's an old saying that if you get 5 people in the room and ask them about a painting, you'll get 5 different opinions. Why? Because people are all different. We all associate different people, things, and events with different thoughts. And if one person gets a joke and another doesn't, it doesn't mean that there's anything wrong with either of them. It means they're interpreting things differently due to different life experiences. So before you say something or react to something negatively, think about the people you're speaking to. Are they really stupid or ignorant, or are you just seeing things in a different way than they are?