Person A: www.4chan.org/b/image.jpg
Person A: SFWBPWSWTF
Person B: I THOUGHT WE WERE FRIENDS!
Person B: THE HEEEEEEEEEEEEEEEEEEEEEEEEEELL!@
Person A: I warned you, bro.
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.