Nah, it's the very first episode with Toph, and Sokka does it. Aang is looking for an earthbending master, and he goes to a bunch of quack trainers, and a school. After the school doesn't work out, he asks two students about earthbending matches at an earthbending arena, and the students go like "On the island of nunya... nunya business. AHAHAHAHA!" Katara does her thing, scares them, they give up the information, and while they're walking out, Sokka does a "represent" exit and says "Water triiibe."
I think it's called The Blind Bandit.