crackpot
crank
nut **
nut case
fruitcake
screwball

Practically a nut case by the time he was sent down.

Perhaps I had come across as a bitter, scary nut case.

Even nut cases (usually) pay attention to letters from lawyers.

This soldier may be a nut case, but he is still on the side of truth, justice and the American way.

A nut case I know exactly how you feel.

It seems the world is full of absolute nut cases.

Abby, I know you must think we're real nut cases, but we never had children.

Now he thinks I'm some kind of a nut case.

"I don't know what happened, he turned into a nut case."

He was a nut case now, so what if she caught him on his feet.