From the Official Star Wars site...
Long before galactic strife enveloped his native Naboo, Jar Jar Binks was exiled from the underwater city of Otoh Gunga. his main sin: being clumsy in front of the head of his clan. To hear Jar Jar tell it in his Gungan/Basic pidgin, he "boomed da gasser, and crashed de boss's heyblibber, den banished."