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]

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.