The bunching effect that takes place when the sweat from a good workout meets the boxers in the grundle region. Also can be used as an insult.
Man I need to hit the showers I've got Grundlebundle like nobody's business.
or
Man that clerk always thinks im trying to steal , what a grundlebundle.
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.