A made up word used to trick stupid 6th graders.
There is not an "X" word but you can get them so pissed at you. It works best if you get alot of people in on it and act serious like it's a super bad word.
Bob: Hey Whitney have your parents told you the x word yet.
Whitney: No whats that ?
Bob:What ... hey guys Whitney doesn't know the x word.
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?"