insane
in-sane
adjective
Mentally ill; not of sound mind, or extremely foolish, wild, or impressive.
"His behaviour was completely insane."
Thesaurus
Synonyms: harebrained, foolish, mad, fruity, kooky, hebephrenic, balmy, nuts, mentally ill, unbalanced, screw-loose, half-crazed
Antonyms: sane