Is there a word for a person who believes themselves to be smarter than others, but frequently betrays that the opposite is true. For example, when dumb-shaming someone, this person uses their big words incorrectly, but confidently. Know-it all isn't quite right, because there's a chance a know-it-all might actually know quite a lot.
egotist noun. TFD
A conceited, boastful person.
An egotist is a self-absorbed, bragging person. From Latin: ego = I.
Toby, vigilant about his diet and insecure about his height, is persuasive as a well-meaning egotist. The New YorkerJun 27, 2019
I was going to say bullshit artist but I think by far the best fit is,
mansplain[ man-spleyn ]
verb (used with or without object)
(of a man) to comment on or explain something to a woman in a condescending, overconfident, and often inaccurate or oversimplified manner: He mansplained to her about female friendships.
to comment on or explain something to someone in such a way: I know some women who are guilty of mansplaining.