Couldn't pour water out of a boot with instructions on the heel

Meaning

This is an elaborate way of calling someone exceptionally stupid or slow. The image of the instructions on the heel makes it clear that the person is beyond help.

Mocking, colorful

Used in a sentence

• I tried to show him how to use the mower, but he couldn't pour water out of a boot with instructions on the heel.
• He is such a dullard; he couldn't pour water out of a boot with instructions on the heel.
• Don't bother training him, he couldn't pour water out of a boot with instructions on the heel.