Bear in mind that Dylan is a sleazy arsehole, his nicknaming for Carly is less a sign of a genuine affection than it is a sign of how highly he thinks of his position in her world. Frankly it comes across as the overstepping of one's station but he is the villain. In short, he's a prick.
Well, at the end of the movie, everyone had a nickname: Dylan - Duchess. Carly - Angel. Sam - The Messager.