When you're taking a shit and jerking off at the same time, right before you're about to ejaculate you stand up and cum on your turd. At this exact moment either your mom, girlfriend, sister, or any female oriented human must walk in on you. Only then will it be a true plunderbluff
"I'm grounded for two weeks.. my mom totally caught me in the middle of a plunderbluff"
when you're holding up your phone and making faces at it, as though you are taking a selfie, but you're really taking a picture of the person across from you or the wall or anything else that seems interesting but you don't want to be caught dead taking a picture of.
This action is often made more convincing by wiggling the eyebrows or opening the mouth, to pretend you're trying to get a Snapchat filter to work.
FRIEND A: "Did you just take a stealthie of me?"
FRIEND B (turning phone around): "no I was just using snapchat's new filter, see?"