That was a pea-brain decision.

Don't be such a pea brain; you could have finished the project on time if you'd focused.

Her pea brain remark derailed the entire meeting.

During the meeting, she quietly muttered that the pea-brain had deleted the file.

Don't expect much from those pea-brains; they barely managed to follow simple instructions.

Calling my coworkers pea brains during the meeting was a mistake I regretted.