Not Too BrightOne worth keeping
“He couldn't pour water out of a boot with the instructions on the heel.”
Can't manage even the simplest task.
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.
Not sharp at all.
He's lost whatever sense he had.
Can't tell the most basic things apart. Even a dog knows those two.