completely stupid or crazy, often in a way that is dangerous:
That's an insane risk.
The whole idea sounds absolutely insane to me.
Why did you do that? Have you gone insane?
someone who is insane is permanently and seriously mentally ill so that they cannot live in normal society:
The killer was declared criminally insane.
people who are mentally ill:
a hospital for the insane
to make someone feel more and more annoyed or angry, usually over a long period of time [= drive somebody mad]:
My little brother's been driving me insane all weekend.
She giggled insanely.