Perhaps due to the miniscule size of his penis, from a young age Sebulba was an overachiever. Excelling in any sport he signed up for, Sebulba was quick to make it through the ranks of nobodies and distinguish himself as one of Tatooine's finest(which isn't saying much). A much applauded alumnus of the Darth Darth Binks University(for the not-so-gifted and downright unfortunate) Sebulba's spectacular success in sports however, did not carry on into his academic career. He continued to attend fourth grade classes well into his middle age.
He did not, however, let this stop him from beating up other kids, being the most popular a*hole in town, and of course taking all the girls. He considered Anakin his greatest rival in all things, which when you consider that Sebulba was 40 and Anakin was only 9, was actually really, really, sad.
Anyway, because of this rivalry, when Watto paid him to bump off Anakin in the Boonta Eve podrace, Sebulba readily accepted. The pod was one of Watto's own design, and subsequently blew up, knocking Sebulba out of the race, and giving him his first loss ever in any sport. This would become a trend.
Sebulba would require massive plastic surgery both for his injuries and also so he could fit into the new podracer format. He visited a surgeon on Tatooine, but not a reputed one, so as a result he ended up looking like some sort of cross between a Frog and a Turd. This was bad cause not only did he start to lose matches, he lost all his women as well.
Dejected, Sebulba retired and enjoyed a brief stint as a minor character in an animated film series revolving around Darth Nerd. Eventually Sebulba saved enough money to buy his own planet, only to have it destroyed by Darth Vader who wanted to pay him back for all that bullying he had suffered as a child.