唇舌

I feel like I’m just wasting my breath trying to explain things to him.

我觉得跟他解释简直是白费唇舌。

Those who protested against the president's decision were actually barking at the moon, since they were in a powerless minority.

由于他们属于软弱无力的少数, 他们反对总统的决定际上枉费唇舌。