Using the free Starbucks coffee house wireless internet access without going inside the store to order coffee.
I drove my car to Starbucks, pulled into a parking spot up front, kept the motor running, whipped out my laptop and did some starjacking. I emailed all my friends for free!
To post on social media first someone else's sad news or story or announce someone else's bad news before they have had chance to post or were waiting a bit because it was still to painful or a secret. To hi-jack someone else's bad news. To hi-jack sadfishing. To gain sympathy and likes yourself, taking sympathy and responses away from the person who it actually happened to.
e.g. "John was going to tell everyone that he had a tumour but his mate Paul sadjacked him by posting about it first" or "I heard my mate's friend had died and sadjacked him by posting the news before him" or "some **** is sadjacking my cat's death on fb"
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?"