Might as well explain the whole story in a history thread.
I wanted a stage name, and my girlfriend at the time suggested px since I always put that when I got off or something. Px is short for Pax, which in English means Peace. I was a christian rapper so I figured it would work. Pax is also latin, which is the language only the high class could read and speak in Jesus' time.
I started putting px cuz when I would put pz people would call me a poser, which got really annoying. I would miss the z and put x by accident a lot, so I just kept putting px. I invented my own style, and now people copy me.