What do I mean by two names?

Throughout my life I have had a large variety of nick-names. Names like Mahana (this is not after "Mahana you ugly", it is after the Mahana that is later in the movie who is worth 10 cows and not 8), Mufus gufus dufus, Mahna, Whetter, Mejica, Mexico, and most recent, Mand (randomly started by my neices Nick and Nat). Of all of these nick-names the one I find the most interesting is one commonly associated with the name Amanda, Mandy.
Where did it come from? Most of the Mandys' I have met, who actually have Mandy written on there birth certificate, have been asked at least a thousand times if their real name is Amanda. I am not complaining. Infact, I am one of the many Mandy's who is fortunate enough to have Amanda as my real name. However, It was not until recently that I discovered how amazing it is to have two names that the public recognizes as names.
For as long as I can remember I have been known as Mandy; at home, and at play, and in all public settings. On returning from my mission however, I decided to start using my real name a little more often. It has been an interesting experiment. Most of the time it takes me a while to figure out people are talking to me. When it finally clicks, I suddenly become more aware of how I am behaving. For like a second I suddenly think I have to behave like an adult.
The look I get from my friends that know me as Mandy when someone else calls me Amanda is a lot of fun to see. They first look at my work or school buddy with a look of disbelief that they actually just called me by my real name. Then they give me a look that seems to ask "who do they think they are calling you Amanda". I also have those friends who know me as Mandy, but think it is fun to call me Amanda just so they can see the confused look on my face as I try to figure out who they are talking to.
I love my two names, and all the other ones I have been called. I think everyone needs an alternate name, as well as a nick-name.