piss up a rope
1. 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 pissing up a rope, so I just don't bother. My mom and dad spent years pissing up a rope trying to get my brother to take his studies seriously; in the end, he dropped out anyway to pursue a career in music.
2. exclamation Get out of here! Leave me alone! (Used especially in the phrase "Go piss up a rope!") Go piss up a rope, pal! No one wants to hear you talking for the entire course of the film. Terry: "John, do you think you could lend me 50 dollars?" John: "Go piss up a rope, Terry. You still haven't paid me back from the last time I lent you money!"