not all there
see all there.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
Examples from the Web for not all there
The bored expression in the eyes—the rabbit, not-all-there expression—gave place sometimes to another look.Day and Night Stories