A boneheaded action committed by one who should knowbetter but goes ahead and does it anyway.
Stupidacity is as stupidacity does! May that dude rest in peace for running a stop sign in front of that semi truck that pushed him broadside into the train running alongside him.
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?"