a phrase used to describe and forewarn a girl who is giving you a blow job or hand job that you are about to cum. most often it is a phrase said just before "blast off" while receiving a blow job, however, it can also be used as ejaculation takes place if you want the girl to be somewhat suprised.
because the term is not very studly, it is not meant to be used to impress the girl, but just just to lighten the mood of a sexual encounter and make the sex more lighthearted, casual, or less romantic by adding some dumb comedy to things.
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?"