That's part of the reason why I still can't close the book on Snape entirely. Even after he killed Dumbledore, and was fleeing with Malfoy, he refused to attack Harry. Granted, he said that Harry was for the Dark Lord, but he still made no overt action to harm Harry, even to hex or curse him.
When Harry tried to throw the Crucio curse, Snape said "No unforgivable curses from you Potter." and when Harry kept trying to throw other curses at Snape, Snape kept blocking them, and telling (or taunting) Harry... "Blocked, again, and again, and again, until you learn to keep your mouth shut, and your mind closed Potter".
Snape was still teaching Harry, still training him. Snape spent last year training Harry in Occlumency, something which Snape is very good at. This year, they are learning to cast spells without the incantations. In short, if Harry is ever to face Voldemort, he had better learn to block his thoughts, and cast his spells silently.
I don't doubt that Snape hates Harry, but I think it is his mission to train Harry to face the Dark Lord. I think what Snape was saying, in essence, was "You think I'm bad?, wait until you face Voldemort!". And his comment regarding the Crucio curse was his attempt to keep Harry pure, to keep him from using an unforgivable curse.