slip on a banana skin

To make a silly, embarrassing, or avoidable mistake. They were completely dominating the game until the quarterback slipped on a banana peel and threw an interception, which allowed the momentum to shift in the opposing team's favor.

COMMON If an important or famous person slips on a banana skin or slips on a banana peel, they say or do something that makes them look stupid and causes them problems. Most of the nation would enjoy seeing mighty Manchester United slip on a banana skin in front of millions. You can be walking across Westminster Bridge full of noble thoughts at one moment and slipping on a banana peel the next. Note: You can also call something that causes someone to look stupid or have problems a banana skin or a banana peel. Insiders watched in horrified fascination as the President lurched from one banana peel to another. Note: Comedies and cartoons traditionally show a character slipping on a banana skin, falling over, and looking foolish.