when you are taking a poop in a public place and someone walks in and you dont want them to hear you in the stall taking a loud poop so you clinch your butt to be quiet
i was in the bathroom at micky d's the other day with mud butt and some guy came in the room i was really EmbarASSed
Taking the limp penis and pushing in back into you as far as it can go. Then you take the loose scrotum (best when out of a hot-tub or hot shower) and fold it from under, on to the top of your penis therefore resembling a turtle hiding in its shell.
The Embarassed Turtle, the Bat Wing, and the Brain are some of my favorite penis molding techniques during boredom.