@weiwei,
When someone uses the term 'monkey around', it implies they act clownish and/or in a silly or mischievous manner...like a monkey.
Banana skins... used in many comic scenes are often put in someone's path to make them slip and fall (a common scene in a TV or movie) to bring a pompous person down to make them look a bit foolish and evoke laughter.
So banana skins would indicate some device that's used to make someone or something lose its footing, trip up or malfunction.