“You,” Snape exhaled, and his face was colorless, “are not to be believed.”
For some reason this line really struck me as very Snapish. Even if he had wanted Harry's advances I can see him being absolutely appalled that 'the boy' went that far.
I love that Snape used Harry's cloak to sneak in to see him-it's sort of how I know things will end up working out, somehow.