The title given to someones brother of sisters boyfriend if they're not married
Juan: Who's this Harrygeezer?
Tom: Oh he's my sisters boyfriend, that makes him my stepbrother-in-law
Juan: Surely he's your stepbrother?
Tom: Nah fam, he's not married to my sister
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?"