Don't be dumb
Definition
A casual idiomatic expression used to urge someone to avoid foolish or unintelligent behavior, often delivered with a mix of exasperation and affection.
An informal admonition equivalent to 'don't act stupid' or 'use your brain,' common in everyday American English conversations.
Examples
When he suggested betting his rent money on a squirrel race, she sighed, 'Don't be dumb, let's just grab tacos instead.'
Trying to charge your phone with a banana? Don't be dumb—plug it into the wall like a civilized human.
His brilliant plan to impress the boss involved showing up in flip-flops; 'Don't be dumb,' his coworker whispered, handing over real shoes.
She eyed the 'five-second rule' crumbs on the floor and muttered to herself, 'Don't be dumb,' before sweeping them away.