Informal One who claims to know everything and rejects advice or information from others.(noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "know-it-all" in a sentence
"Bert is the quintessential cantankerous old man, a know-it-all with a chip on his shoulder the size of an AARP Magazine cover."
"Not being a know-it-all, just sometimes sexual traits will out themselves!"
"For example, the loud lady with the pink hair came across as a bit of a know-it-all – but was she really, or was it just an act?"