WordNet sense 1 (very foolish):

harebrained

WordNet sense 2 (talking or behaving irrationally):

wild

WordNet sense 3 (characteristic of or suffering from psychosis):

psychotic

WordNet sense 4 (suffering from paranoia):

paranoid

WordNet sense 5 (wildly disordered):

maniacal

WordNet sense 6 (insane and believed to be affected by the phases of the moon):

lunatic

WordNet sense 7 (slightly insane):

touched

WordNet sense 8 (driven insane):

deranged

WordNet sense 9 (insanely irresponsible):

idiotic

WordNet sense 10 (affected with madness or insanity):

crazy, demented, disturbed, mad, sick, unbalanced, unhinged, brainsick

WordNet sense 11 (informal or slang terms for mentally irregular):

daft