When a cute, adorable young child that everyone thinks will grow up and still be attractive looses their cuteness at some point and turns out not attractive. It is the opposite of a cocooner.
"Did you see that picture of Chris when he was 5 years old as his profile picture on facebook?"
"Yeah! Wasn't he the cutest child ever?"
"It's too bad he's a reverse cocooner..."
"I know right? I feel bad for him."