When they say that, reply “caca”? as though you aren’t sure you heard them right.
Watch their heads explode and then explode again when you say, “Oh, sorry - for a minute there I thought we might be in agreement.”
In my house we have an agreement. If the libs in the family don’t talk politics, we won’t call them idiots. We don’t even bother arguing. “You’re an idiot cousin Hal” and we let it go at that.