Upset the apple cart.
[Idiom] UPSET THE APPLE CART. - Discover How to Express Disruption in Fluent English
disrupt a plan
When someone 'upsets the apple cart', they do something that causes a plan, order, or a stable situation to go awry. The imagery that the phrase evokes is clear: a cart full of neatly stacked apples being toppled, with apples rolling everywhere, creating chaos. This idiom is often used when a person's actions inadvertently or intentionally cause a carefully arranged plan or situation to fail, leading to a disorderly or troublesome outcome.
Example Sentences
Their unexpected arrival upset the apple cart.
Their unexpected arrival disrupted plans.
He tends to upset the apple cart with his comments.
His comments often cause disruption.
Changing plans now would upset the apple cart.
Changing plans now would create a disruption.