One sandwich short of a picnic

Meaning

This is a polite way to call someone slightly foolish or not very bright. It suggests their mental basket is missing a key ingredient required for a successful day.

Playful, mildly mocking

Used in a sentence

• I love my brother, but he is one sandwich short of a picnic when it comes to fixing cars.
• The new manager seems one sandwich short of a picnic if he thinks we can finish this project by tonight.
• Don't mind him, he's one sandwich short of a picnic but his heart is in the right place.