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. It looks like I'm spitting into the wind trying to get a raise from my boss.

spit in(to) the wind

To do something totally pointless, fruitless, or futile; to waste one's time doing something that will not or cannot come to pass. To be perfectly honest, I feel like voting is just spitting in the wind, so I don't even bother. My mom and dad spent years spitting in the wind trying to get my brother to take his studies seriously; in the end, he dropped out anyway to pursue a career in music.

spitting in (or into) the wind

a futile or pointless activity.

1996 Daily Telegraph Both the Church report and the atheist professor are spitting in the wind, of course, because the incoming tide of superstition has a long way to rise yet.