be pissing 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, I feel like voting is just pissing in the wind, so I just don't bother. My mom and dad were pissing into the wind for years trying to get my brother to take his studies seriously; in the end, he dropped out anyway to pursue a career in music.