bricks shy of a load - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Mentally impaired, either unintelligent or merely eccentric. For example, He may be handsome but he's not too bright—a few bricks shy of a load. This term, transferring a light load to lightweight mental capacity, is usually preceded by either a few or a specific number such as two. [Slang; 1960s]