I don't know if it would be described as a rule, precisely, but I watched a friend of mine handle a situation similar to what you describe.

Dann was the chief engineer at the radio station where I worked, and he was the most intuitively gifted computer person I ever met. He and computers just seemed to click. He taught me a lot about computers at the time (early 1980's), yet my knowledge was insignificant compared to his. One day an acquaintance of his stopped by, and I listened in to their conversation. It didn't take long for me to figure out that Dann's friend was pretending to know a great deal more about computers than he really did. Even I, with my pathetically limited knowledge of the subject, realized that this guy was saying things that were just plain wrong, in an attempt to impress Dann. Dann just listened, nodding his head, saying things like "That's interesting," or "I hadn't thought of it that way before."

When the fellow left, I asked Dann how he could just sit there and listen to all that stuff and not straighten the guy out. Dann said, "All that would have done is embarrass him, it wouldn't have accomplished anything and might have damaged our friendship. Eventually he'll figure those things out on his own, meanwhile it's better to just let it be."

I've always admired that standard of behavior that Dann set, and try (with limited success) to emulate it.

tanstaafl.