go piss up a rope
It's like " go take a long walk on a short pier". It would be very hard to piss up a rope. It's also like telling someone to "fuck off" or "go get lost". A widely used term in the 50's and 60's by men who worked in factories together for extended periods of time.
Shakey was so mad at Ralph that he told him to "go piss up a rope". Ralph was so stupid that he actually obtained a large piece of rope and proceeded to urinate on it while it was held in a vertical position.