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Phrase(s): rock the boat
1. Lit. to do something to move a boat from side to side, causing it to rock. (Often in a negative sense.) • Sit down and stop rocking the boat. You’ll turn it over! 2. Fig. to cause trouble where none is welcome; to disturb a situation that is otherwise stable and satisfactory. (Often negative.) • Look, Tom, everything is going fine here. Don’t rock the boat! • You can depend on Tom to mess things up by rocking the boat.
McGrawhill's American Idioms And Phrasal Verbs
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Disturb a stable situation, as in An easygoing manager, he won't rock the boat unless it's absolutely necessary. This idiom alludes to capsizing a small vessel, such as a canoe, by moving about in it too violently. [Colloquial; early 1900s]
American Heritage Idioms