WCheese is a general term used to describe something (usually when you cannot think of anything else). It can also be used to enhance something, to greet someone, or to insult someone.
Gimme dat wcheese. You smell like wcheese. What up wcheese? She was all like wcheese.
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?"