The whole thing is a bit of a injoke.
(Specifically, some bar in God knows where, New york. a few years ago.)
Me and my former-stepcousin (the Former- part is a even longer story) were messing around in the under-18 part of that bar, and he called me a poopskin (i was like, 8 at the time and i had just discovered the internet). i thought it was funny at the time, and decided to register at a forum (for a game i liked) with that as my user name, and the -The-Liar part comes from another game i like. Since then, i really haven't thought of anything better. Besides, on the other forums i go to, Changing my name (once i thought of a better one) would be as rough as the Bell -> AT&T transition.