Wow! This was certainly entertaining. I will admit that my wife and I named my son with the plan that he would use his middle name. His first name was the name of the ancestor that first arrived in the US. The ancestor's first son was named after him. This continued until someone decided to move the name each generation (first/middle/first/middle). I explained this to my wife (after we were married) and told her what our son's first name should be. She mentioned that there were probably too many people with that name, so she would agree only as long as we called our son by his middle name. We agreed and it was done. HOWEVER, my son wasn't in on the agreement--we went to school one time when he was in fourth grade and his teacher kept referring to a child we didn't know. Finally, we realized she was referring to our son by his first name. We informed her of his "go by" name, then, when we returned home, asked our son why he hadn't said anything. We had moved to a new town and he felt the teacher was quite attractive and very nice, so he didn't want to make her feel bad when she used his first name. Therefore, everyone that went to school with him in that town calls him by his first name.
As someone noted, it is also a great opportunity to find out who really knows you. I called a great-aunt one time that I had never met. When I finished explaining who I was, who I was trying to reach and how I discovered her name, she laughed and said "I know you have to be family. No one has used that name for 60 years other than family and you couldn't make up the names of the three people you mentioned." We had a great conversation after that.