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1 definition by Quine

 
1.
A demand to be a man and to stop acting craven or cowardly. A derivation of man up (which in itself is a derivation of cowboy up), although more insulting. While man up can be used as encouragement to do something, sack up is almost always a challenge to cease doing something that should be beneath you
"Oh sweet mother of god! The terrorists are going to blow us up with Snapple bottles!" _This_ is terrorism's A-game? Sack up, people.
by Quine August 13, 2006
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