Mansplaining is much more specific than men showing off; it's men assuming women are clueless and talking over them (e.g. the prototypical case where a man explained a woman's book to her, oblivious that she wrote it).
The benefit of making up words to dismiss people is that you get to make up the definitions too. "Mansplaining" means whatever is convenient at the time. This is why it is preferable to use real words and ignore people who make up nonsense words.
Which I don't think is the issue here at all...