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.
(..) I couldn't find my Buzz. I know I left him right there. Honey, I'm sure he's around. You'll find him. It's too short! We need more monkeys! There aren't any more! That's the whole barrel! Buzz, the monkeys aren't working! We're formulating another plan! (..)1995 Toy Story