A prank wherein a person farts into an empty pillow case or bag, then unexpectedly places this bag over another person's head, then punches them in the stomach, forcing them to frantically gasp for air and inhale the nasty fart. Best practiced with a team of three, two of whom hold the victim in place, while the lucky third does the farting/punching.
"Fred was being a total douche, so we all got together and gave him the Shanghai Shroud. You should have seen his face when we farted in a pillow case and then placed it over his head, then punched him in the stomach. He inhaled that fart like a champ."