Occurs when small amounts of poop accumulate from not wiping well enough. Eventually the poop hardens into a crust. After an event that causes the individual to perspire the crust melts to form rumple butter. It is distinguishable by its intense odor that may resemble anything from a fresh turd to the bottle return room at your local grocery.
You're playing basketball with some friends and something begins to smell so bad that your gag reflex becomes an unavoidable reaction to the odor. You know that it's not a fart because although a fart may linger for a moment it eventually dissipates. You notice there is no trash or fecal matter present and you begin to deduce that this could be a classic case of rumple butter. Tell your stinky friend to clean their ass out. Rumple butter... Spread that on your toast in the morning... Mmmmm