Why are people from the US so rude to me?

Whenever I go to the US (I'm from UK) I tend to go to lectures and events that require taking notes. Being my own forgetful self, I only pack a pencil and some paper, nothing else. So when writing down what the lecturer is saying, I often make mistakes in my notes and ask the person next to me or a teacher or someone: "Could I please borrow a rubber?" or "Do you have a rubber? I could really use one right now!" or something along those lines. And I'm really polite! But they just give a dubious look and ignore me! I mean, people do make mistakes whilst writing, they can't expect me to write perfectly all the time and not need to rub out anything! Why am I treated this way? :(