Mine is the Japanese pronunciation of an exboyfriends gaming name. He had a lot to do with getting me into gaming and at the time I thought it was totally cute (being that I am Japanese American) to have the same name as his but in Japanese. Unfortunately the relationship didn't last but I enjoyed the name enough to keep it.
Shinda Usagi= Dead Rabbit
Mine is just a nickname based on my last name. I've had it ever since I was a kid. (And after trying to use it at different websites, I realized that other people with my last name must also use the nickname.)