What is Crank?

Legal Definition
A term vulgarly applied to a person of eccontric, ill-regulated, and unpractical menial habits; a person half-crazed; a monomaniac; not necessarily equivalent to "insane person," "lunatic," or any other term descriptive of complete mental derangement, and not carrying any Implication of homicidal mania. Walker v. Tribune Co. (C. Ct) 29 Fed. 827.
-- Black's Law Dictionary