The hitchhiker in question is Tom Joad, the protagonist of the story. At the beginning of the story, he is freshly paroled and is returning to his family and his father's 40 acres of land. While walking down the road, he spies a truck stop and decides to stop for a moment. He sits on the running board of a truck that is clearly marked for "no riders." Meanwhile, the truck driver pays his bill for and loses his change in a slot machine. He claims that lottery machines are rigged so that no one can win.

When he goes outside, Tom asks him for a ride. The driver points out the "no riders" sign, but Tom tells him that sometimes "a guy'll be a good guy" even though some "rich bastard" put a sticker on his car.

By saying this, Tom is appealing to the truck driver's sense of good will and his shared disdain for the poor financial situation of the many compared to the fortune of the few. The truck driver has just experienced a moment where he feels that the financial system is completely "rigged," so he is more inclined to help someone who seems down on his luck.