This mixup was found in the following newspaper:
It is a congruent conflation of “to rub salt in the wound’ and “to add insult to injury”, both meaning to deliberately make someone’s misfortune or unhappiness worse. “Wound” and “injury” are similar meaning words, probably creating the mental mashup. Now if the writer had written “add-in salt to injury” that would be an eggcorn. An eggcorn is a similar sounding phrase spelled differently. Because of the similar sounding words, this is a very common malaphor, with over 2,300,000 hits, according to Google. A big thanks to Eve for spotting this one.
This beauty is a mash up of “rubbed salt in the wound” (make someone feel worse about something) and “rubbed his nose in it” (remind someone of something one has done wrong). Perhaps the speaker was reminding someone of a mistake and bragging about it at the same time. Or maybe this is a new form of medical treatment? A big thank you to Ed Brady for hearing and sending this one in.
I heard this one by Willie Geist on the Today show. He meant to say “you’re just rubbing salt in the wound” as he was explaining that the person’s actions were making the situation worse. As for the other expression, not sure but certainly sand is abrasive and can hurt if in a wound. It also conjures up in my mind the guy kicking sand in the other’s face, aggravating the situation.