Inserting your penis, dildo, strap-on, fist, ect. inside someone's ass while they are pooping to push the poop back up their ass.
The man put his penis inside the girl's ass right as the poop started to come out, causing the poop to go back in her ass and causing them both to have a not so pleasant feeling but the great feeling of knowing that you accomplished it.
-he is mud plunging her, he mud plunged her, she plunged herself, I mud plunged that filthy whore-
(hint: it would make your life easier for you if you didn't tell people that you mud plunged someone)
Right before your girl needs to take a big dump you push your cock in her ass until shit comes out the sides like cheese-wiz. Then you ram it balls deep repeatedly. The shit makes good lube!
Note: Never attempt the Mojave Mud Plugger if she ate anything spicy the night before.
Ann wasn't being a good girl so I gave here the Mojave Mud Plugger.