Every woman has had this experience: Some guy descends from his great height of manhood to explain something to you about which he knows relatively little and you know about 100 times more.
This is mansplaining: "To explain in a patronizing manner, assuming total ignorance on the part of those listening. The mansplainer is often shocked and hurt when their mansplanation is not taken as absolute fact, criticized or even rejected altogether."
The Urban Dictionary explains that it's not only men who do this, and Madame L has indeed had the same experience with women.
(Madame L hastens to add, as does the author of this wonderful and true story of having some man do some mansplaining to her about a book she herself had written, that she has enjoyed the friendship and companionship of men who are not guilty of mansplaining and who in fact have been wonderful, helpful, appropriately humble, and so on. And Madame L must confess she has been guilty of mansplaining, once or twice at least, and hereby promises to stop. Including not writing any more about mansplaining. )