where it hurts 

In a boy's / man's case, then nuts / balls, head or asshole.

In a girl's, / woman's case, that can be her titties / boobies, head, or asshole.

Boy 2: Girl 1 kicked Boy 1 where it hurts! What a bitch-ass mothafucka!
Girl 1: I kicked Boy 1 where it hurts because he kicked me where it hurts.
Boy 2: Oh ok.

where it hurts by RetroGalacticGamer April 5, 2020

Rub Your Paycheck Where It Hurts 

Response given to someone who is annoyed at all the extra time they've been putting in at work even though they are being compensated for it.

Rob was whining about putting in a 60 hour work week so I told him to "rub your paycheck where it hurts"

Rub Your Paycheck Where It Hurts by Calihog July 27, 2009

hit him where it hurts 

To hurt someone where you know it'll be painful the most

Ima hit him where it hurts, his family.

hit him where it hurts by John Williamson September 13, 2017