Last year, I had two unusual class name phenomena. One class had duplicate names (most students shared a name with one other person). Another class comprised a majority of students who preferred to be called by a nickname as opposed to their given names.
In my summer job, I had twin girls who's first names both began with the letter "D". They didn't look identical, but they always sat next to one another. Six weeks with those kids and I still couldn't tell you which was which.