According to MultiVac (Asimov's brainchild) jokes are part of an elaborate alien experiment and all humans are lab rats. Apparently this is why we cannot remember where jokes come from and we are unable to make our own.
But I have tried:
Q: what did Arial whisper to Times New Roman?
A: I am font of you
But then MultiVac also says puns are all that we are capable of and they don't count
Hmmmmmm.......
