One of my favorite things, right up there with whiskers on kittens, is to take well-known pun-based jokes and paraphrase them so the pun and therefore the humor is lost. I always find the paraphrased versions funnier than the originals. I don't know why I have this sick compulsion. It's interesting, in light of the whole translation question ("Poetry is what's lost in translation"). Jokes often don't translate. So why are these so funny to me? Obviously, it's dependent on my knowing how they're supposed to go (though even if I didn't, I could probably figure it out). Anyway here are a couple. (If you haven't heard these can you guess the real joke?)
Q: What did the Buddhist say to the hot dog vendor?
A: Do you have Tofu Pups?
Q: How is light beer like making love in a canoe?
A: It's fucking practically water!
Now that I think about it this basically works on the same principle as the Back to the Future line "Why don't you make like a tree and get out of here."
Can you think of any more of these?