Rob doesn't know Alex and Alex doesn't know Rob EACH OTHER
Rob and Alex don't know each other.
The coach respects the players and they respect him. EACH OTHER
The coach and the players respect each other.
I don't understand you and you don't understand me. EACH OTHER
We don't understand each other.
I'm not speaking to my sister and she isn't speaking to me. EACH OTHER
My sister and I aren't speaking to each other.
My brother's shouting at my sister and she's shouting at him. EACH OTHER
My brother and sister are shouting at each other.