Synonyms : looney, loony, nutcase, weirdo

Example : A man who had gone mad.

Synonyms : brainsick, demented, disturbed, mad, sick, unbalanced, unhinged

Example : A crazy scheme.
Half-baked ideas.
A screwball proposal without a prayer of working.

Synonyms : half-baked, screwball, softheaded

Example : The crowd went crazy.
Was crazy to try his new bicycle.

Example : Had a crazy dream.
Wore a crazy hat.

Example : Crazy about cars and racing.
They are dotty about each other.
Gaga over the rock group's new album.

Synonyms : dotty, gaga, wild