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.
spit (out) the dummy
To have a childish overreaction or angry outburst to a negative situation or outcome; to act in a bad-tempered manner, likened to a temper tantrum of a child. "Dummy" here refers to a plastic teat used to soothe teething infants (also called a "pacifier" in the U.S. or a "soother" elsewhere), which they may spit when in the middle of a tantrum. Primarily heard in Australia. John spat the dummy when I told him I'd sold his old comic book collection. Don't go spitting out the dummy just because Cheryl got the promotion instead of you.