Just explained this yesterday in another thread.
I'm a Mortician/Funeral Director. When my boyfriend and I started going together he would introduce me to everyone as Morticia. It was really funny because even though some knew what I did for a living, they never figured out it was a joke until one day he called me by my name, which is Laura. Some figured it out when they finally found out my profession.
My sister hosts a chatroom on another site and I always went in there as Morticia. Over the course of time, it got shortened to Morti.