A geography brain hurty of a slightly different kind:
We'd been studying tourism as a topic and were about to start a case study on tourism in Turkey. For the life of me now I can't remember how it came up, but I made some comment about the capital of Turkey being Ankara.
Up pops the other class know-it-all: "No it isn't! It's Istanbul."
Me: "Err, no - it really is Ankara."
Her: "You're wrong. It's Istanbul. EVERYBODY knows that."
Me: "Err, no. Look - our atlases have Ankara marked as the capital."
Her: "Well they're wrong."
Fortunately for my sanity (unfortunately for the other 23 people in the room, who'd been watching/listening to this conversation like spectators at a car wreck), the teacher arrived at that moment and opened her lesson with a brief description of Turkey, including the name of the capital.
I half wondered if the other class know-it-all would continue to argue, but apparently she'd accept information if it was given by the teacher - just not from me, even when I was backed up by a respectably published atlas!