I've been toying around with ideas for what reason Jar Jar might be banished for with my version. I really liked Magnoliafan's explanation that he was supposed to guard the "Kaiburr Crystal," but he fell asleep and it got stolen by human thieves. It tied in nicely with the ending, and set up where the resentment between the humans and gungans came from.

A more scoundrel-ish explanation that I heard someone suggest a long time ago in a galaxy far far away, was that Jar-Jar got caught in some illicit activities with Boss Nass's daughter, and was promptly kicked out of Theed. I had some ideas for some dialogue that I thought were amusing, although I'm not sure how appropriate it'd be for a Star Wars film so I may end up just borrowing Magnoliafan's Kaiburr Crystal explanation. Also, while the concept of Jar-Jar and Boss Nass's daughter amused me, the fact that we'd never see her would be problematic.

"I know you're just humans, but you shoulda seen 'er! Built like a mermaid, that girl is!"