Cas smiled, grateful for Sirius's good humor. "So," she started, "it can be safely assumed that you lot aren't plotting to bring the house down then? Because, in that case, I am in full favor of a boycott and enjoying the festivities, and not thinking about the impending doom of graduation and having to earn a living." She paused, catching her breath, then continued on with a gently sarcastic "I see you've worn your best dress robes. I'm impressed, Sirius, thoguh you're making me feel underdressed. On a less facetious note, it is a nice shirt you've got on."
All jokes aside, she was glad to see him. Assuming he didn't have a date, James didn't show his face, and he didn't incite any sort of shouting from Lily, it could in fact, be a fun evening.