If you took a look at my birth certificate, you'd see that my first name is John, my middle Mark, and my last Gurney. That was not really how my parents wanted it to happen. My parents couldn't agree upon my name. My dad wanted John, and my mother wanted Mark. So they compromised, and wanted to call me John Mark.
So, my name was John Mark, but around 8 years old or so, people would think Mark was my last name and call for Mr. Mark. We decided to hyphenate my name to John-Mark so that they wouldn't get as confused.
I still have problems w/ people calling me Mark John, or John Paul (as in Pope John Paul which I hate), though it has gotten better now that I am an adult. I guess most people don't pay enough attenting to a sub-eighteen year old's name.