Definition
to make someone understand something, especially when they have been told many times before and the speaker is annoyed
I don't know how to get it into your thick head that you can't use your phone during meetings!
You need to get it into your thick head that I'm not changing my mind; just give up already!
I’ve been trying to get it into his thick head that the report needs to be submitted on time, but he doesn’t seem to listen.