What is the most WRONG thing a teacher, professor, or school book told you?

Fun story! A while ago a sort of mexican version of The Onion came around called Deforma (a parody of popular newspaper "Reforma"). Their breakout article said that Mexico's national anthem was acquired by the chinese government, and as such would no longer be public domain. It's a bonkers story, yet a lot (And I mean a lot) of people bought it, including a significant portion of my teachers. I think hearing my maths teacher complain about it is one of my core memories now