So in high school I had a couple other nicknames that were riffs on my first name, Ross, and I didn't like any of them. So when hanging out with a rather silly but eloquent friend we decided that I needed a new nickname. We bounced around a few, one of which being Rosstafarian which I use whenever Rosstopotamus is too long. It happened to be near Christmas and we were listening to Christmas songs and the song "I Want a Hippopotamus for Christmas" came on so we switched Hippo with Rossto because adding a t there helped it roll off the tongue better, since then I've used that as most of my online aliases. I have never found anyone anywhere that has the same username or anything remotely close and I also really like the name because it incorporates my real name but adds a bit of silliness and flair. There's actually a sign hanging in my room that was painted by my now fiance' that incorporates the name and it is one of her favorite nicknames for me.
P.S. My fiance' is also pretty active here on the server :)