The Tourist is a woman who was on a tour bus.
While Homer was driving Red Barclay's truck to Atlanta, he learned that there was the Navitron Autodrive system in the trucks, so vehicles can drive themselves. He showed off the system to Bart by climbing out onto the truck's hood while it was driving. Bart climbed too and the truck then was passed by a tour bus. One tourist on the bus looked out and called out: "Look, nobody's driving." The other tourists quickly looked out and Homer told them that everything would be fine because the truck can drive itself. He also told them not to tell anyone and the tourists started taking photos of them. The bus then drove off.