Aww, Boss Priest is the perfect, doting grandfather. He's kind, levelheaded, patient, and very reasonable. He's the type of guy Lucius matures into by the time he's retelling us his eleven-year-old adventure story.
Boss Priest represents the typical Southern gentleman. He follows the traditional customs surrounding contracts and agreements, and he keeps up his gentlemanly way of interacting with other gentlemen.
When he appears on the sidelines of the racetrack, he's not angry or upset over the events of the past four days; instead, he provides some moral insights that can only come with wisdom and age. "A gentleman can live through anything," he says to Lucius, for example. "He faces anything. A gentleman accepts the responsibility of his actions and bears the burden of their consequences, even when he did not himself instigate them but only acquiesced to them, didn't say No though he knew he should" (13.120).
Well, this makes Lucius bawl, but the two come to the agreement that since Lucius has learned a considerable amount throughout his adventures, it's all good. In the end, Grandpa Priest can't be too mad. And mad he isn't—we think he's just relieved he got his car back.