For what it’s worth, I corrected my teachers on a number of occasions all through school. The one that stands out in my mind, for some reason, goes all the way back to sixth grade.
I came in one morning, and the previous evening the teacher (Mr… um… thinking… oh yeah, Lester) had apparently spent some time redecorating, because there was a new display on the front bulletin board. I don’t remember exactly what it was, but I do remember that the headline, across the top of the board, made in big letters obviously laboriously hand-cut out of construction paper, was “The <Something> Effect,” referring to some science principle we were about to begin studying. Except, of course, that he had spelled it “affect.”
For the first half hour, I remember not paying attention in class, simply staring at that display and trying to determine if he meant what he had done, and that he was using the noun “affect(ation)” in a weird way, or if in fact it was an error as it seemed to be.
Finally I decided to ask. During a period when we were supposed to be reading quietly, I raised my hand and asked Mr. Lester to come over. In a whisper, I referred to the display and suggested that “affect” should be “effect.” He frowned at me, so I opened my desk – I remember this part clearly – and pulled out my personal Webster’s Collegiate. While he looked over my shoulder, I looked up the two words and verified the definitions as I remembered them. He didn’t really say anything (other than a muttered “okay, thanks,” before walking away), but the next day it was fixed. Nothing was ever said about it again.
I suspect it went as well as it did because I kept it quiet and didn’t call anyone else’s attention to it. Had I asked more loudly, or God forbid in front of everybody, it might have gotten ugly. I already wasn’t especially popular with most of the teachers at that school; my parents had had a couple of run-ins with the principal regarding policies of treatment for advanced students, and I myself was kind of a smart-alecky know-it-all. (What do they say about early formation of personalities?) Publicly correcting a teacher would have been a significant Career Limiting Move, I think.
So yeah, based on my experience, I agree that the approach of finding him after class, alone, and saying in a nonthreatening manner, “That Big Bang thing was a joke, right?” and then generally proceeding with the assumption that he was formulating a witticism that was too arcane for the class to grasp, is probably the best bet.