Can robots have a sense of humor?

Cracking jokes is not the same as digging them. I've been working around AI for 30 years and haven't yet seen an AI system able to explain what is funny about a given joke. I'm not talking about pre-programmed answers, like the ones you can find in Siri: if you ask "What's the meaning of life," you'll get a funny answer, like "A good life is about wearing clean and dry clothes," as this answer was put there by a human programmer; the system doesn't have a clue about why this could possibly be funny. Notice that the three questions are ordered in increasing difficulty levels, which perhaps is counterintuitive to many of us because creating something is supposedly more difficult than understanding something. But in this case, the opposite holds true, as we'll explain.