Larry the Cable Guy on Blue Collar TV uses this as a sort of catchphrase. It's meaning is pretty much universal, but is mostly used as a way of agreeing with something enthusiastically.
Son: Hey Dad, do I plug in the leaf blower now?
Dad: GETERDONE!
Dude1: Dude, that chick is so hawt!
Dude2: GETERDONE!
no,no,no. You folks got it all wrong. Trust me I was there when this happened. To deflower a young woman.
The girl wanted me to have sex with her friend. She shut the bedroom door and said," When she comes out of there I want her split like the Grand Canyon. Geterdone."
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?"