I was always verrrrrrry possessive about my food. I didn't want anyone to touch it. My wife learned that it wasn't the right thing to do to stick her fork on my plate while I was eating. If I offered it fine, but don't just reach for what you want.
My nephew got a fork in his hand for doing that. I told him many times not to do it. But he kept it up. I knew how to cure him. I stuck a fork right into the top of his hand when he reached onto my plate. He's never done it since.
I don't share utensils, water bottles, glasses, etc... with anyone.