Mike Portnoy from Dream Theater's catchphrase. He even hid it in a song in morse code. And he says it a lot too. I find it hilarious, and it can be used in the way you think it could be used.
Teacher - Now, you guys have a 10 page essay due in a week. Muhahahahah!!!
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.