First off, look at dirty sanchez and pay close attention to the definition that says u wipe the poop with ur finger or thumb, now this is basically the same except u take your 2 pinkys and make a French type moustasche on her face and could even be equipped with the proper French noises.
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?"