The Ravenous Bugblatter Beast is so mind-bogglingly stupid that it thinks that if you can't see it, it can't see you. Therefore, the best defense against a Bugblatter Beast is to wrap a towel around your head.
Alas, my great aunt Susan was devoured by a Ravenous Bugblatter Beast of Traal. She did not have a towel handy. And they are very very ravenous beasts.
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?"