by the short hairs

have (someone) by the short hairs

To completely control, dominate, or hold power over someone, especially in a difficult or awkward situation. A reference to the hairs on the back of one's neck, though it is often (and incorrectly) assumed that the phrase refers to pubic hairs. Can also be used with the verbs "got" or "catch." After scoring a third goal in the last quarter, the home team really had their opponents by the short hairs. He found out about my painkiller addiction and is using it to blackmail me—he has me by the short hairs now.
See also: by, hair, have, short
Farlex Dictionary of Idioms.

by the short hairs

Under one's complete control. This expression is often used with get or have, as in She had her husband by the short hairs. It is in effect a euphemism for have someone by the balls, the hairs in question being pubic hair. [Colloquial; second half of 1800s]
See also: by, hair, short
The American Heritage® Dictionary of Idioms by Christine Ammer.
See also:
  • have (someone) by the short hairs
  • have someone by the short hairs
  • get (one) by the short hairs
  • get/have somebody by the short hairs
  • have (one) by the short and curlies
  • have someone by the short and curlies
  • a tough spot
  • a tight corner
  • be in a tough spot
  • be in a tight spot
References in periodicals archive
Also irritating are the frequent references to modern critics (Jakobson, Foucault, Barthes, Kritzman, Derrida, Bloom), who often seem to be dragged in by the short hairs to support a claim that needs no supporting.