A combination of the words "under," "stand," and "that." It is commonly used in military training environments, on the streets (primarily the hood), and Louisiana.
I'm going to ripyo' soul out yo' chest and eat it for dinner, unastanat?
"Bro, haven't you submitted your UCAS choices yet?"
"I don't know whether to go with Bath, Lancaster or Warwick."
"Dude, stop UCAStinating and choose one."
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.