a few sandwiches short of a picnic

a few sandwiches short of a picnic

A pejorative phrase meaning not very intelligent or of questionable mental capacity. It can appear in many different forms and variations (for example: a few bricks shy of a load, a few cards shy of a full deck, etc.). He says he's going to start a business selling bees as pets. I think he may be a few sandwiches short of a picnic.
See also: few, of, picnic, sandwich, short