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.
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