My full name is “Richard Timothy Cunningham”. I shorten it to “RT Cunningham” when and where I can. Some people even call me by my first two initials. It started when I was at my first Marine Corps duty station. People would call me from across the room with only “RT”. I didn’t pick my nickname, they did.
I’ve had many nicknames over the years. My parents called me “Ricky” when they were still alive. I always hated that nickname and I still do.
Some people call me “Rick” or “Dick”. Very few people call me “Richard”. I’ve also been called many other names over the years that I don’t care to repeat.