It probably depends on the person and how much they insist on going by their full name or not. I have a cousin named
Christopher that usually only goes by
Chris around friends. To our family he's always been
Christopher, mainly to distinguish him from his mother's cousin,
Kris, for whom he's named after. He usually introduces himself as
Christopher and people naturally shorten it, he just goes with it though.
I've also known a
Matthew,
Elizabeth,
Nathaniel,
Benjamin,
Kaitlin,
Kathryn,
Christine,
Christina,
Angela (2),
Madeline (she's around 12 now, refuses to be called
Maddie, I'm so happy about that!),
Victoria, and
Anneliese (so glad she goes by her full name, it's gorgeous). But those are few and far between, the majority of Matthews I know are
Matt, Benjamins are
Ben, Kaitlins and Kathryns are Katies, Angelas are
Angie, and so on and so on.