A: You should not have criticize your son in front of his friends.
B: Why? He did something wrong.
A: I know. But at that time your blame is rubbing salt into his wounds.
A: I only wanted to help him.
B: But it is not the right time.
rub salt into one’s wounds
该习语的字面意思是“往伤口上撒盐”，引申为“火上加油”“雪上加霜”““加深某人的创伤”等意思。 其英文解释为：to make a difficult situation even worse for someone。
To rub salt into her wounds, he began to laugh at her.
Losing was bad enough, having to watch them receiving the trophy just rubbed salt into the wound.