The corncob guy was a resident of Ba Sing Se who rode the monorail from one place to another. He came across as rather peculiar to many people, as he typically bore a vacant expression with a corncob sticking out of his mouth.
While riding on the Ba Sing Se Monorail in 100 ASC, the corncob guy briefly crossed paths with Team Avatar. Ironically, thanks to his off-the-wall appearance, he showed up just as Sokka was expressing some rather irrational fears of his to the rest of Team Avatar saying, "Weird stuff happens to us." His unexpected presence prompted a bewildered reaction from the group as he unceremoniously wedged himself in the seat between Sokka and Toph, all the while sucking on a corncob.