The most stupid thing I ever heard in school was during english class.
The teacher told us about famous english literature and mentioned "Alice in wonderland".
When I told her I had read the book and its sequel called "Through the Looking-Glass" she said I was wrong to say the book had a sequel and no matter what I said completely refused to believe "Through the Looking-Glass" existed!.
So for the next time we had english class I rented both books from the library and presented them to her with the whole class present.
20 years have passed since I took that class but I think her face is STIL red with embarrassment
