"I'm not!" Rincewind declares indignantly. "I've got the bronze octagon and everything! Impersonating a wizard is very dangerous where I come from, especially if the wizards find out." He glares as best he can. "And I've thought of something to demonstrate as well. Just don't say I didn't warn you!" He crosses his arms in an attempt to match Severus' stern an menacing look. He fails quite miserably.