Via Tyler Cowen, the first one is a truly excellent joke … I almost think I started laughing before I got to the end of the line:
It’s hard to explain puns to kleptomaniacs because they always take things literally.
This was in the comments, and the punchline got me but good:
A physicist, a biologist, and an epistemologist are asked to name the most impressive invention or scientific advance of modern times. The physicist does not hesitate—”It is quantum theory. It has completely transformed the way we understand matter.” The biologist says “No. It is the discovery of DNA—it has completely transformed the way we understand life.” The epistemologist looks at them both and says “I think it’s the thermos.” The thermos? Why on earth the thermos? “Well,” the epistemologist explains patiently, “If you put something cold in it, it will keep it cold. And if you put something hot in it, it will keep it hot.” Yeah, so what?, everyone asks. “Aha!” the epistemologist raises a triumphant finger “How does it know?”
And yes, I added (a politically incorrect) one to the comment thread.