mine is relatively simple:
when i got hooked up to the internet the first time (back in greece...awww..i owe a lot of knowledge to the guys at magnet.gr), the admins decided to use the first 8 chars of my last name as a login. my last name is "von Schweinitz", and since the "von" is considered a title (sometimes - it's rather complicated!), they took the "schweini", and it kind stuck.
if you ever see a german speaking monk or cybernaut snickering at my handle, then you maybe interested in the fact that "schwein" is german for "pig".
just imagine how bored i am of stupid jokes about my last name.
every freakin' day.
but, actually, "schweini" could be read as "piggy", which makes the whole thing at least a bit cute (especially since i'm 2.05m tall).
what bugs me a lot is that there's this other "schweini" lurking around in the 'net somewhere...but some research turned out that his real last name is "schweinichen", which sounds even more ridiculous in german, so he's excused. :-)