Foil
Character Role Analysis
Jack and the Older Man
Jack seems to be pretty much the opposite of the hard-drinking protagonist. While the older man has no trouble throwing back whiskey (sometimes while double-fisting with a beer), the younger man gets quickly and thoroughly drunk—and tells everyone so (though no one seems to care or really believe him). He also doesn't share the younger girl's interest in getting frisky on the bed, but the older man seems to feel the opposite. In fact, he encourages the young girl's interest.
Finally, the young man is at the beginning of his relationship, and the older man is clearly at the end of his—that is, they're at opposite ends of the same journey. So this duo is definitely the story's central foil pairing.