That person, normally a female, who defines everything that warrents your scorn. This term should only be said to the person it describes if you know you will never want anything from her (or him), including, but not limited to, sex, booze, sex with her sister or friend.
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.