When you go to cook up some potatoes but you forgot what potatoes are and you think they are poisonous you don't cook or eat them and after a while they grow so big that the house explodes.
Try not to be potato forgetful today or this house will be no more.
Oh no, There was a dude that was potato forgetful today and made the building explode, Silly potato forgetfulness people.
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?"