Stands for very fucking good. Pretty much self explanatory. The F is for extra emphasis on the good part, or to express anger, agony or put a stopper on a cocky bragger's mouth.
Marvin said, "I got top marks in the SATs!" Sarah retorted, "Vfg."
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?"