get/have somebody by the short hairs
get (one) by the short hairs
To acquire complete control, dominance, or power over one, especially in a difficult or awkward situation. A reference to the hairs on the back of one's neck, despite popular misconceptions. Can also be used with the verbs "have" or "catch." By scoring a third goal in the last quarter, the home team really got their opponents by the short hairs. He found out about my involvement and is using it to blackmail me—he's got me by the short hairs now.
get/have somebody by the short ˈhairs(also get/have somebody by the short and ˈcurlies) (informal) get/have somebody in a position where they must agree to what you want: We can’t go on strike because the boss will simply hire new staff. He’s got us by the short and curlies.
Short and curlies refers to the hairs on a person’s body.