few cards shy of a full deck

Adjective

 * 1)  Mentally deranged; demented; insane.
 * That guy might be a few cards shy of a full deck — he thinks that substitute sugar is really a government tracking system.

Synonyms

 * See Appendix:Snowclones/few X short of a Y
 * See also Thesaurus:insane.

Antonyms

 * See also Thesaurus:sane.
 * See also Thesaurus:sane.