hank freak, n. — Green’s Dictionary of Slang

hank freak n.

[? the masturbator ejaculates into a handkerchief; or ? hank n.⁵ (3)]

(US prison) a compulsive masturbator.

1967

M. Braly On the Yard (2002) 154: It was probably some rapist turned hank freak who was cutting the sex scenes from the L and L books.