Conceding for the sake of argument that God does exist and that Jesus will one day return, what do you really think would happen? If someone all of a sudden started claiming he was the son of God come back to life, would we all bow down in worship or would we send him to counseling and probably have him committed to a mental hospital?
First off, your signature has the quote "why are you so surprised I came back?" in it, and that made me laugh due to the topic.
Secondly, this is actually an interesting question. The most interesting answer, I think anyway, is actually the Muslim answer: that Jesus (who is not the son of God but merely a prophet) will return to the earth upon the eruption of a war between muslims and non-muslims (which arguably, we already have - though it's hard to argue) and that Jesus will fight on behalf of the Muslims, bringing with him a terrible beast to destroy the non-believers.
I think that, if Jesus were to really return to this earth without slaughtering us all, he'd have a very difficult time of convincing us it was him. There is a quote somewhere in the bible of him saying 'I am not a show magician' or something similar, so I think he'd refuse to do so and therefore be labelled a "looney".