Being an ESL teacher, one hears all kinds of interesting interpretations of the English language. Thankfully my students are adults, so correcting misinformation is a little easier most of the time. But I do hear some funny things!
On a test: the correct answer to the question was: Being a police officer is more dangerous than being a teacher.
The most common answer given by students: A police officer is more dangerous than a teacher.
(Which may or may not be true, depending on who has the Taser, but that's another story!)
In class: "Teacher, why did my friend tell me it isn't correct to say 'I knocked up your door'?" (Well, there is the problem of splinters!)
During a shopping role play exercise, practicing expressions for refunds and exchanges: two students (women) have chosen to use a pet store for their practice. They have gone through meerkats, puppies, cats, and birds, when I overhear this exchange: "I'd like to exchange my beaver. It isn't friendly."
When I discreetly explained the idiomatic use of that particular word, they blushed beet red...and went back to the same example, giggling madly while the rest of the class kept asking "What? What?!"
I told them to ask the students in question, after class.