My name is Casey.
In 1997, I told friends that I was going to make a rap album. My rap name would be "KcMastuhPeace", and the rap album would be called "MastuhPeace Theatuh".
I even made a few (mock) rap songs. Like how "I'd rap you in my rhymes with the mix-masta sauce."
After that, I made an email that only allowed ten letters.
"KcMsterpce" was born.
After playing Counter-Strike with that handle, and then playing MMORPGs where people recognized my name because it had "Kc" in it somewhere (Darkcaress, Kcorblios, etc...), it's just stuck with me.