you + appositional name, phrase, or clause

   With this kind of vocative expression the speaker typically expresses surprise or regret that what he or she is saying must be said to this particular person, as opposed to someone else. ‘You of all people’ sums up that thought. One man might say to another: You robbed me; you, John!’ where the intonation pattern would be the same if the speaker continued ‘the friend I trusted most’.

   That clause might in fact take the place of the name, as might the phrase ‘my best friend’. For that matter, the vocative ‘you’ in such an utterance could be expanded by any number of appositional components. You robbed me; you, the man who is god-father to my children, the man I have always treated as one of the family, the man I thought I could trust completely, who swore to me that I could always rely on him,’ etc., etc. It would of course be possible to say: ‘You robbed me; the man I trusted most!’ omitting the second, vocative ‘you’. In this case ‘the man I trusted most’ retains many vocative qualities, if not all of them.

   As such an expression is lengthened, however, getting further away from pronominal ‘you’, most speakers would be tempted to support it with a vocative ‘you’ somewhere in the string. There would also be a strong tendency for such expressions to become a third person substitute for ‘you’ in a kind of echo of the original thought: ‘You robbed me: the man I trusted most robbed me!’ This is not true of normal vocative expressions, and the kind of vocative phrases and clauses mentioned above clearly belong in a category of their own.

   A literary example occurs in The Portrait of the Artist as a Young Man, by James Joyce, which has:‘“You should be ashamed of yourself,” said Father Arnall. “You, the leader of the class!”’