Sometimes saying nothing is the reply that makes them rethink what they said.

Silence after something out of line gives the sentence back to the person who said it. They hear it again in the quiet, with nothing to argue against, and a lot of the time that is when they notice what they said. A reply, any reply, gives them something else to focus on instead.

You do not have to plan this or make it pointed. Just let the gap sit for a few seconds instead of rushing to fill it. If they come back and soften it, you were right to wait.