A greeting to a friend who is leaving a party or social gathering when it's the first time you've seen them all night, even though you've both been at the same party the whole time.
Derek (appearing suddenly from other room): "It's getting late dudes, I gotta jet. Catch you later."
Jon: "Hey Derek! I didn't know you were here. Alright guy, what's-up-see-you-later."
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?"