have someone/something by the short and curlies
(alsohave someone/something by the big brown ones, …by the curlies, by the short hair(s), ....by the shorts, ...by the wool, ...where the hair is crisp, …where the hair is short, ...where the wool is tight/worn off the top of his head) [the image of grasping the victim’s pubic hair]
[late 19C+] to have someone at an extreme disadvantage, to control completely.
[1920s+] (Aus.) to know a subject extremely well.