A comparison of some sort with one person to another. Can be used in a serious or funny manner.
Nancyl McToot sees a photo of her friend who got a BBL and says to her sister showing her the picture- "Kim Kardashian WHO??" This could or could not be a complement.
Billy sees his brother who has green paint on him and says- "KERMIT THE FROG WHO."
Jillian looks at her mother who fell in a puddle of something blue and says, "Papa Smurf WHO."
Bob got some round glasses and his brother looked at him and said, "Harry Potter who?"