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.