Back in the good ol' days of Call of Duty 4: Modern Warfare, there was a level where you go through Chernobyl with a dude named Captain MacMillan. So I thought, "What about CaptainMacMuffin?" I shortened it to McMuffin so that it showed up ingame in MP, and the name just stuck.
I occasionally get the odd, "Bro, you're a fatty for naming yourself after a thing at McDonalds." 1. MckyD's sucks terrible bawls, and 2. I didn't even think about that when I made it so yeah.