very strange or foolish:
She’s the craziest person I’ve ever met.
[ + to infinitive ] You’re crazy to rent the place without seeing it first.
Crazy can mean mentally ill.
Crazy can also mean behaving in a strange way esp. because of stress, as if you are mentally ill:
The constant whine of the machine nearly drove (= made) me crazy.
I think she’ll go (= become) crazy if she doesn’t take a vacation soon.