what does it mean letterally ? not the meaning.
Here's the literal meaning.
rub in, move your hand or a cloth over a surface while pressing down firmly; press to and fro against a surface; apply an ointment or polish with a rubbing action.
Source: The Little Oxford English Dictionary
Here's the idiom.
rub it in
If someone rubs it in, they keep talking about something that makes you feel embarrassed or upset. I know I made a mistake, but you don't have to rub it in.