When I created my username years ago, my mom had Molly, I had a cat named Lucy, and a foster pup named Cassie.

It's the first letters in their names.. Mol = Molly, Luc = Lucy, Cass = Cassie.
MoLuCass. That's how I first started to write it when I came up with it..
My mom still had Molly, and I still had Lucy when I joined here, but Cassie was adopted out..
I like this username, so I just keep it every where.