The storm 'threw a monkey wrench into' their plans for a picnic. [=the storm ruined their plans for a picnic]
After many years of disappointment, she finally 'got the monkey off her back' by winning the championship.
Our teacher warned us not to try any 'monkey business' while she was out of the room.
(..) It's going to be payback for anybody who crosses me. We have a crisis here and you stroII in an hour Iate? If I must put up with-- Back off, monkey boy... or I'II teII your dad you treat this pIace Iike your piggy bank. Or we shouId caII the IRS... and arrange a vacation for you at CIub Fed? (..)1994 The Mask