A toothless beggar or homeless man.
A mumblecrust shouted something at me today, but I didn't understand him.
by Reubenalexander July 03, 2011
The gross crusty white shit that forms in the corners of old people's mouths when they talk.
That teacher had such bad mumble crust that I had to drop the class.
by Dopegirls September 14, 2010