The last name thing isn't just military or sports, actually. I think it's often just a guy thing.
My brother was LastName in high school, so I (a year behind) became "LastName's Sister" to a lot of the drama kids we hung out with, until I earned a nickname of my own (DeadBethy, from croaking on stage as Beth in Little Women). Then our younger sister made it to high school, so she became "Little LastName" (which was amusing as she was taller than me).
Now I work with corporate attorneys. We're all nerds. About as far from a sports or military setting as you can get. And they call each other by last names.
I think part of it stems from the fact that there tends to be a smaller variety among the male names. So we have several guys named "Joe" and it's just easier to refer to them as "Johnson" and "Smith" -- even though they're partners and basically our boss.
Whereas I am the only Giraffe they're likely to run into. I do love having a relatively rare name. :-) But I'm still LastName and GLastName and GL about 50% of the time.