Mud Toaster

In short, it's another phrase for the act of spitting hot sludge from ones sphincter and further leaving a crust along the outer edge of ones rim.

More specifically, after eating unusually spicy cuisine, a very hot slush of fecal juice makes its way through the large intestine (toaster) and amalgamates with a solid preheated log to form a mushy substance (mud). This mud is then baked for as long as the sphincter can handle.

At the point in which one can no longer clinch, the mud spits and/or spews from the turd cutter leaving behind a crust along the rim. This is when you know that you've cooked the mud long and hot enough for a toasted crust to form.

This causes anal leakage, or what many people know as mud butt.