I only have one named fish, a neon called "Claude". This is because I have five neons, but every time I look there are four. And I look, and I look, and I'm just about to start searching around the tank for a jumper when, lo and behold, there are five. That fifth neon is Claude, because I swear he has the power of invisibility.
Admittedly, I'm not entirely sure it's always the same neon, but I'm pretty sure it is.
My flatmates have also instituted the custom of calling dead fish Bob. This happened during the period when I didn't know about cycling and lost quite a few fish. They started calling all the dead ones Bob, and referring to fish dying as "ascending to Bobdom". I'm not sure why, since none of them ever bobbed around on the surface, but I can't shake it now. Fortunately, there have been no Bobs in my tank for a while now, and I certainly hope that continues to be the case.