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?
Best Answer
I agree with @FumbleFingers, that repeating the personal pronoun is empathic repetition. It is only slang and should be omitted from formal writing; at present and for the near future. It implies that you are putting an emphasis on the fact that this person is a sly dog, and they probably beat you at something. It can be used to vent this feeling, and it is used by some people in speech to express this.