rub salt in the wound
Definition from Wiktionary, the free dictionary
Alternative forms 
Derived from the stingingly painful sensation of table salt deliberately being rubbed into an open, bleeding wound, as for torture, interrogation, etc.
- (idiomatic) To make an injury feel worse.
Usage notes 
- For rub, one can substitute verbs such as add, pour, put, possibly requiring a change in the preposition in.
- See salt in the wound for variations in that portion of the expression.
to make an injury feel worse