Interesting. I'd thought this chapter gave us evidence of Snape being evil, because a greater-than-or-equal-to-double agent should think immediately of disguises that need to seem real. And if we assume he's not evil then he probably sympathizes with Hermione's anti-bullying campaign. But he might not go against Dumbledore if DD didn't want to use the debt. (Still seems slightly sinister that he didn't tell Harry secretly. But not much, given their history and the likelihood Harry would think of it anyway.)