Butt sand
The sand and dirt particles you find in a couch or chair when you lift the cushion.
Oh my, there is a lot of butt sand in daddy's chair.
butt sand
The sweat-soaked flecks of toilet paper that accumulate in ones' butt crack during the day. This term applies mostly to women as men's butt cracks usually contain large amounts of poop and other filthiness.
He asked me to clean off my butt sand before he would go down on me.