Symbolism, Imagery, Allegory
Before we start talking about the flagpole skater, take a look at this video clip from 1932.
Wow, right? You can imagine why "everyone in town was more or less affected by the skater" (19.4). Henri even sees "philosophic implications" (17.5), and you know what? When an author just tells us point blank that something has "philosophic implications," we kind of have to spend some time thinking about what they might be. Granted, it's Henri—Mr. Chicken Feathers and Nutshells—who's saying this, but still, we've got to look into it.
First: The flagpole skater is hired by Holman's Department Store to promote a bunch of sales they're having. So he's up there for days and days in order to help Holman's make money. That seems significant, especially considering the narrator's and characters' general attitude toward money: having a little is okay, but wanting more will just mess you up.
No surprise, then, that Mack and the boys, who don't care much about money, also don't care much about the flagpole skater: "Mack and the boys went up and looked for a moment and then went back to the Palace. They couldn't see that it made much sense" (19.4). Maybe what they're seeing is that the crazy things people do for money—like sticking a poor skater up on a flagpole, or worse, agreeing to be the poor shmuck up on a flagpole—just don't make much sense.
Second: the skater is "a lone man on his platform" (19.2). Sounds kind of heroic, doesn't it? He's literally on a pedestal, like a sculpture of an important person. Unlike a sculpture, though, this guy is a living human with certain … needs. Like a toilet.
Here he is, this heroic-looking figure, braving loneliness day after day. But people keep giggling when they think about him because they can't figure out how he goes to the bathroom. The flagpole skater, then, seems to symbolize the hollowness of this ideal of the lone hero. Maybe the real heroes here are guys like Doc: living right in with the prostitutes and bums, not skating in ridiculous circles high above their heads.