When the word sick doesn't fully explain the sheer awesomeness of a certain thing, condition, or situation. It is used to expand on the popular term by expressing how something is actually sick to mind bottling proportions.
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.