Some people really know a lot and they can come across as arrogant (like the fictional character Sherlock Holmes-people like that). Watson could have despised Holmes for almost showing off his knowledge but instead Watson grew to respect Holmes. So Holmes is a know it all type who really does know a lot but this character also admits it when he doesn't know something and he respects people who best him or who know things he doesn't know or didn't observe (he always respected Irene Adler for example).
Others are blowhards who only care about their ego. Holmes would admit it when he was wrong but these types are reluctant to admit being wrong. They blame others and they are very critical of everyone but themselves (they are hypocritical). These types are bullshit-ers; they fake knowing everything.