be spitting in the wind
be spitting in(to) the wind
To be doing something totally pointless, fruitless, or futile; to be wasting one's time doing something that will not or cannot come to pass. To be perfectly honest, when I vote, I feel like I'm spitting in the wind, so I usually don't bother. If you're trying to lose weight without changing your diet, you're spitting into the wind.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
be spitting in the wind
If someone is spitting in the wind, they are wasting their time by trying to do something which has little or no chance of success. As an approach to the problem, this is scarcely more than spitting in the wind.
Collins COBUILD Idioms Dictionary, 3rd ed. © HarperCollins Publishers 2012