In few occasions I've heard that actors and characters in tv add another 'you' when they are talking to somebody else resulting in an odd "you [insert something here] you" -sentence.
Example: Guy 1: "I finally did it!" Guy 2:"You sure did, you sly dog you!"
Questions that bother me: What is this sort of sentence/idiom/expression called and what is it for? Is it proper language or slang? What does it imply and why would you use it?