I won't eat an apple unless it is cut up
That feels very odd, why don't you like whole apples?
I had a bad experience with a whole apple at a young age
Fruit is good for you no matter how it is, if it is whole or in pieces. As long as you are eating fruit it is good for your health.
I'm not going to listen to you. I'm an adult and I know what I like and what I don't like.
Well, you sure have the right to eat whatever you like and don't like, but it s not right for you to dismiss me and ignore what I have said as I am here to help you. If you treat people this way they may feel very hurt by it and they may end up avoiding you.