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 sandwiches short of a picnic, 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 bricks short of a load. The new manager is nice enough, but he's a few bricks short of a full load, if you ask me.