Not Too BrightOne worth keeping
“The cheese done slid off his cracker.”
He's lost whatever sense he had.
In the same vein
All Not Too Bright →Dense. All weight, no sharpness.
Looks alert. Isn't.
Not enough sense in there to do the smallest job.
Can't manage even the simplest task.
Not sharp at all.
Can't tell the most basic things apart. Even a dog knows those two.