hit where it hurts

hit sb where it hurts (most) (to do something which will upset someone as much as possible)
— больно задеть, обидеть, задеть за живое; ударить по (самому) больному

Example 1: She hit him where it hurt most—in his bank account. (CALD)

Example 2: If you want to hit her where it really hurts, tell her she's putting on weight again. (CALD)

Example 3:.....

Related vocabulary:
[задеть за живое]