Harvey, it's an oldie and often with the variant I posted. Basically, go piss on yourself....as it's impossible to piss up a rope and do otherwise. Many add like I do, a "slack rope" to be absolutely sure.

Similar to things used instead of saying "Shove it up your ass." Such as, "Put it where the sun don't shine" or "Make it all brown." Just variations on a theme.

Spaw