Someone who is insane is severely mentally ill.
Some people simply can't take it and they just go insane.
一些人就是接受不了,于是便变得精神错乱。
If you describe a decision or action as insane, you think it is very foolish or excessive.
He asked me what I thought and I said, 'Listen, this is completely insane.'
他问我是怎么想的,我说,“听着,这愚蠢至极。”