the intentional slurring together of the English words forget + about + it toward the effect of expressing surety, wonder or degree of approval; the usage is largely associated with New York soldiers of the mafia.
The physical space where you forgot why you left one room to go to another room to get whatever it was you wanted, sometimes forcing you to go back to the first room. Maybe several times.
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?"