frost a rock
v. phr.— «A Cal Adventures, University of California at Berkeley, is the practice of (get ready!) frosting a rock.. At Colorado Outward Bound and the National Outdoor Leadership School in Wyoming, the same procedure is called, yet more graphically, smearing. A hiker rises from an afternoon nap…and then proclaims to all present, “I think I have to go frost a rock.”» —by Kathleen Meyer How to Shit in the Woods Aug. 1, 1994. (source: Double-Tongued Dictionary)