One who is generally dumb and does not understand references to simple subjects. Usually abbreviated to F.S.
Me: Dude, Johnny just got Glenn Beck and Ed Hardy confused.
Friend: What an Flour Sack!
Me: I know! He's a total F.S.
Friend: What an Flour Sack!
Me: I know! He's a total F.S.
by DaRumblyTank February 10, 2011