Ziz said:
Mine is a portion of my last name. Real first name is John. In high school, we had about four Johns in the class so everyone - including ourselves - took to calling us by our last names or some variation thereof, mostly out of necessity to avoid confusion over who someone was talking to or about. It stuck.
I had this issue myself in high school, except we had about four Eriks in the class (though I was the only one that spelled it with a K).
I became known as "Pancakes."