1. to be extremely knowledgeable or experienced.
2. a person who acts as though he/she knows everything and overwrites (DISMISSES) the ideas, opinions, comments and/or suggestions of others.
by Mr. Terrence L. Trezvant October 5, 2003
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A person who's quick to interrupt the actions, comments, or approach of others on just about everything they say and do, so as to disapprove in some way and try to correct them with their own views on the topic
"Ann: "I think Jerry needs some tylenol and-"

Pat: "No, No, Ann! When someone feels that way, you need to get them some chicken noodle soup."

Elaine: "Well, I'm going to feed the bird so-"

Pat: "NO, NO, ELAINE! For a bird like this, you only feed it three to four times a day and you want to give it honey."

Ray : "I'm going to run out and get some tools to-"

Pat : "Ray, that's rubbish. To fix a bicycle, you have to use old dirty tools. New tools don't get the job done these day. It's the old fashioned kind that will get the job done."

Janice : "Pat, quit it. You're being an motherfucking know it all. Quit it. QUIT IT!"

by Leo Bos July 20, 2008
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A person who thinks they are all that and a bag of potato chips. They correct people all the time in an annoying, rude way.
Mother , father, and daughter are in the room.
"What is wrong." Father asked.
"I'm sick. I don't feel so good." mother answered.
"It' s not ,'I don't feel good', it's I don't feel well "daughter said.
"Don't be such a know it all" said the mother.
by sour grapes i hate kias December 31, 2016
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pejorative One who makes it appear as if they're an expert on a subject while there are also signals (subtly or blatantly noticeable) that this person doesn't know very much on the subject or at least as much as they're acting like they do on the subject; pretending to have much knowledge on a subject matter
(Note: there are countless ways to seem knowledgeable on a subject as by behaving correctively and correcting people all the time, giving unwanted advice, expressing opinions as fact, not accepting advice or information from others, etc., but when there are also indicators that one doesn't know what they're talking about, they're considered a know it all or engaging in know it all behavior)

"Even though I'm only fifteen and I've never held a job before I want you to listen to me carefully; on your interview, if you're not sitting cross legged, they won't hire you. If you don't nod, they won't hire you. Employers hate when you don't wear a tie. Companies these days aren't into what's on your application. Employers these days are real into the whole look aspect of it all. Take it from me," said my know it all son before I handed him his schoolbag and replied, "Shut up and go to school, dear!"

I found it shocking that some know it all bum out on the street was telling me how to handle my taxes the right way.

I try very hard not to seem like a know it all when discussing scientific matters; I provide evidence and back up what I'm saying and explain to others of my college experience in the field. That way, people regard me as knowledgeable and not a know it all.
by Rick Warwick August 28, 2008
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Someone who thinks they know everything that is to be known. They argue about things that they have no knowledge about. They either act like they know or they really believe they know what they are talking about on any given subject. They are arrogant and believe they are always right. See arrogant, hard-headed
I know what a know-it-all is because I am one.
by Meen5 September 10, 2011
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1. One who's always acting as if things that are abstruse or not necessarily easy to understand are pointedly obvious, and often shows a snobbish hostility towards others if they're not showing complete understanding of it:

someone who treats you like an idiot for not knowing difficult things or acts like difficults things are obvious is a know-it-all

2. One who expresses their unproven opinions and ideas as if they're obvious known facts as if others should have known a long time ago.
"Hahahahaha! Trigonometry. That old stuff. You're having a tough time with that," laughed my know-it-all sister, Megan.

"Well students. You actually have to discern the entomological aspects of it." "Well, DUH! No shit, Sherlock. If you can't, that's pretty sad," said a know-it-all in the class.

"I don't get how to fix the TV," said my father. "Omg! You don't know how to fix a TV set. Lmao! Who doesnt know how to fix a TV set, take it apart and put it back together again. That's so obvious."

Abby said "no duh" to nearly everything she heard during the study on insects. She is such a know-it-all.

"All you do to fix it, is turn it off and then tighten some of the wiring. Duh," said Kya. Kyra had never tried fixing a computer in her life. She was just acting like a know-it-all.

by MikeZatin July 11, 2008
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an offensive term for an arrogant person who professes to know everything in 1 and only one subject but in reality they know absolutely nothing in that subject.
please do not confuse a know-it-all with a pundit, or someone that is blowing fairy dust up your skirt. they are 3 completely different things.
by Sexydimma August 6, 2014
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