ladrar a la luna

1.
SpainLatin Americageneralneutralcolloquial
- To perform an action or make a complaint that is pointless because it will have no effect.
- To express frustration or protest in a way that is futile or will not be heard.

Examples:

ES: Nos lo han puesto hoy, bueno ayer, pero la línea hoy, que sin línea... es como ladrar a la luna.
EN: They put it in yesterday, and we got the line today. Without that, it's like barking at the moon! We're in the book.
ES: Supongo que no hay derecho a que traten a nadie así. Pero decir esto es como ladrar a la luna.
EN: I suppose it's completely wrong to treat anybody like that, but saying that is like barking at the moon.
ES: - Puede ladrar a la luna.
EN: - He can bark at the moon.