What is knowitallism?

Someone who knows it all and is brown with a white Subaru

Levi the knowitall said he watched two dogs sucks each other off and they both came at the same time because he fingered their buttholes

knowitallism - meme gif

A person who acts like they know it all but prove they know nothing.

I paid attention to what they were saying, until i realized he was a knowitall knownothing. Then i told him to shut up.

Guy who puts definitions on urban dictionary to either make someone laugh, or to prove himself right.

Urban Knowitall: guys look on urban dictionary, it has my username! and it says im handsome and rich!
Person: you posted that...

That stubborn little cunt has a serious case of knowitallism, I'd sure like to kick him in the head.