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2.
one who hasn't a clue about anything whatsoever
Edgars: We don't have a pro-shop, sir.

Captain Murphy: Who knows better, me or a know-nothing like you who knows nothing?!
by Michael Belong May 12, 2009
 
1.
a knownothing is the complete and total opposite of a know-it-all. the knownothing sustains itself in social circles by pretending to know what they are talking about and backing up their arguments with nonexistent facts, in the hopes that the individual they are dialoging with are less educated than themselves.

when confronted by a know-it-all, there natural enemy, they become belligerent and any air of wise sophistication is abandoned in favor of insults and off-subject commentary.
Cliff Claven, the most popular and relevant knownothing of his time has been quoted saying things like:

"a pig's orgasm lasts 30 minutes"

"White Out was invented by the mother of Mike Nesmith of the Monkees"

"The word samba means to rub navels together"
by Colony13 February 09, 2009