Originally posted by omgchos
The point i was making was that he wasnt mocking him when he said it. His tone was that of "matter of fact" which goes with the rest of the line. If he were mocking he might have mentioned something of his betrayal.
And dont you think in Return he might have mentiond something of the sith and how everyone who becomes one becomes darth. All he basically said was that he changed his name. Albeit no matter how you look at something someone somewhere will always see it differently, but i never once heard someone refer to him as just "darth" accept obi wan. i only ever heard "Darth Vader", Lord Vader" and "Vader". In fact in the first movie the emperor doesnt even call him darth.
His tone was mocking and confident because he knew if he got killed he could do the ghost thing and still mentor Luke, it was hardly matter of fact. He wouldn't mention anything of the betrayal because there would be no point; to Obi-Wan he's too far gone for anything to impact him. As he says 'He's more machine now than man, twisted and evil' Only Luke sensed the good in him and the conflict. It doesn't matter that only Obi-Wan refers to him as Darth, it is still ambiguous as to whether its an name or a title, it could be any.
Anakin Skywalker becoming Darth Vader does not definitively mean that 'Anakin' became 'Darth' and 'Skywalker' became 'Vader'. None of this is proved in the OT through dialogue or anything else (its all about interpretation) and the argument is somewhat moot as the PT explicitly gives us the fact that it's a Sith title. And the PT is connected to the OT, however badly.