Sounds like the professor was crappy. I'd have said "very well then, have a nice day." Then, at the end of the class, I'd pass around a piece of paper and tell

Sounds like the professor was crappy. I'd have said "very well then, have a nice day." Then, at the end of the class, I'd pass around a piece of paper and tell everyone left to write their name on it. We'll call it the "I'm not a douchebag exam." Everyone present would get a 100, everyone else would get a 0. And then I'd still have that content on the "real" exam.