Okay, I have another one too.
So, this was in first grade and I was about six.
We were talking about what foods were good for you, and we had one of those food pyramids that show you how much of which type of food you should eat every day. My teacher asked us all to name some vegetables, and we all said things like lettuce, broccoli, and carrots. Then she asked us to name some fruits. All the other students said things like apples, oranges, and pears, but I, being the little showoff that I was, said tomatoes.
My teacher replied with, "No, that's not a fruit, that's a vegetable." and I replied, "No, a tomato is a fruit, not a vegetable." We went back and forth like that for a while, until my teacher finally said, "Just pick something else, I'm not arguing about this with you." So, I chose another fruit, but was angry about it the whole day.
The next morning, when I came into school, my teacher pulled me aside and, in a hushed tone, said, "I looked it up. You were right, a tomato is a fruit. I'm sorry." I was so proud that I had been smarter than my teacher. I just beamed at her and said, "That's alright." then went into the class room.
Now, looking back on it, the whole thing was pretty funny and ridiculous, but at that time, I was so happy and proud of myself. I talked about that for years.
