A greeting or farewell said in the period between 12:00 AM (midnight) until 5:59 AM, known as postmidnight, wee hours, small hours, wee small hours, early hours, overnight, zero-dark-hundred, oh-dark-hundred, zero-dark-thirty or oh-dark-thirty.
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.