WAAY back in high school I went to diabetes camp (yes, there is diabetes camp), where each group had to come up with a cheer. The movie "Superstar" had recently come out (dating myself), so at the end of our cheer one girl went "Super-E!" ("e" was the first letter of our team name). After that camp (same summer), I went to a church youth leadership retreat, where I one time charged at another guy and speared him onto the couch (very playfully), got up and said "Super-T!" (you also have to realize I was about 100lbs and very small and skinny, I couldn't actually hurt anyone and all the girls thought I was cute). They all thought that was funny, so I got the nickname Super-T, or often pronounced Supa-T.
So when Wizards of the Coast had message boards (rip) I started posting using a version of Super-T as my handle. It looked like [Supa_T(im)]. After a couple of boards updates they removed the [] and () and became supa_tim. So, I've been using some variation on that ever since. You can find me on most Magic the Gathering message boards with a similar name.
This also explains my avatar. On the original Wizards' boards I picked the picture from the Prodigal Sorcerer because his nickname was "Tim" because people thought he resembled the character from Monty Python and the Holy Grail. So, I've used him ever since (and I have quite the collection of Tim cards as well).