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.

Named for a behavior commonly exhibited by male newbies on internet forums frequented primarily by women. Often leads to a flounce. Either sex can be guilty of mansplaining.

to delighting in condescending, inaccurate explanations delivered with rock solid confidence of rightness and that slimy certainty that of course he is right, because he is the man in this conversation