A Know-Nothing Know-It-All is a character who insists he or she knows everything; is always right; that they were the ''actual'' original creator of an idea; and who generally has an extremely high opinion of themselves and their abilities.
Nothing could be further from the truth. They are grossly misinformed, or just lying, about everything they talk about with authority. They create nothing new, and are Ignorant of Their Own Ignorance. Their abilities could best be described as "scarce". Such people are, in fact, the living definition of the word charlatan.
http://tvtropes.org/pmwiki/pmwiki.php/Main/KnowNothingKnowItAll