have (got) someone by the short and curlies
US /hæv ɡɑt ˈsʌm.wʌn baɪ ðə ʃɔrt ænd ˈkɜr.liz/
UK /hæv ɡɑt ˈsʌm.wʌn baɪ ðə ʃɔrt ænd ˈkɜr.liz/

1.
держать кого-то за яйца, иметь кого-то в полной власти
(informal, sometimes offensive) to have complete control over someone, especially by having an advantage over them or by knowing something about them that they want to keep secret
:
•
The company had him by the short and curlies after he signed that contract.
Компания держала его за яйца после того, как он подписал этот контракт.
•
She knew his secret, so she had him by the short and curlies.
Она знала его секрет, поэтому держала его за яйца.