1) A hard, rocky turd, usually spherical but can be patty-shaped. Just one, no more no less, in the bowl, as if it cracked off a canyon wall.

2) Any kind of stone shaped shit that may or may not tear one's anus on the way out.

3) What almost squished Indiana Jones in his first movie before he deftly dodged it to safety.

4) What can sometimes dangerously develop in one's lowers after eating two whole, nutritious loaves of white Wonderbread simultaneously without drinking a glass of water.
Dude, that butthole boulder you just launched rolled like a stone down the bowl like some underwater pinball machine. See if you can fish it out. We need a new doorstop.
by Wyatt Junker July 10, 2011
Get the Butthole Boulder mug.