Yo: ¿En cuántos países del mundo se habla galés?
Alumno de 1ºBach: Que va, el galés no existe como idioma
Yo: uuuh, yes

Me: Welsh is spoken in how many countries in the world?
A-level student: Yeh right, Welsh isn't a language!
Me: Uuuuuh, yes

More fun from English class with the primary kids:

Me: Okay Javi, show me your food chain
Javi: Here it is
Me: Can you explain it
Javi: That's the grass, that's a wolf and that's a bee
Me: Okay, and how does the food chain work?
Javi: The bee eats the grass and the wolf eats the bee
Me: Uuuum, it's a good attempt Javi, but bees don't eat grass, and I don't think wolves eat bees....
Javi: Yes they do!
Me: Are you sure?
Javi: Yessss, the science teacher said
Me: [time to repeat the problem in Spanish] Vale, pero Javi, las abejas no comen hierba y los lobos no comen abejas
Javi: Clarooooo, pero esto es una oveja, no una abeja
Me: Aaaah, well in that case, an oveja is a sheep and an abeja is a bee
Javi: Ooooooh!

To be honest, the drawing did look more like a genetically modified bee than a sheep!

Me: Give me an example of a verb in the past simple tense....
Boy from 3ESO: Rafa Nadal!
Me: Excuse me?
Boy: Rafa... you know.. Rafael Nadal
Me: Of course I know, but what's he got to do with the past simple?
Boy: Oh, I thought you said tennis.

....Yes, because past simple tennis makes soooo much sense!