n. muffin shaped penis, which at full erection is hard as wood or "lumber". (other definition) n. human feces that is a cause of eating a "Denny's lumber jack slam" with the combination of a muffin.
first example: girl say's to sexual partner "ow! i can't fit that lumber muffin."
2nd example: "dude... i ate at Denny's and had a muffin it took me 30min. to shit that lumber muffin."