When annoyed, agitated or just messin wit someone who is on thier way to annoying you, it siply means "eff-off"
John: Hey Cathy What you wanna do tonight?
Cathy: Go away I don'e LIKE you.
John: You know what forget you.
Cathy: Fine then, Suck my left butt- cheek!
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?"