You guys have hit it out of the park. I have little to add, except that it needs some sort of faux-highbrow literary reference, like Steve Carell's "Proust scholar" in Little Miss Sunshine (raise your hands if you think that screenwriter knows anything Proust other than that the smell of his cookie made him remember a lot of stuff). Maybe Quarter the arcade attendant wins Plunko over with a few quotes from, um... Ezra Pound?
Or Sylvia Plath.
Khalil Gibran
I think hippie grandpa should quote Gibran. Matt, Plath was actually my initial thought, but (1) she's so stereotypically linked with "sensitive' young women, and (2) a lot of the audience might actually have read her. I think that Plunko should be conspicuously coloring the margins of an old paperback of
The Bell Jar with crayons in one scene.
If not Proust, Quarter needs to be into something that a lot of the targeted art-house-but-not-really audience would associate with a sort of marginal coolness but not know so well that it needs to be conveyed with any kind of accuracy. The ur-model of this is Steve Buscemi's collecting 78s in Ghost World (though it probably goes back even further, and yes, I know that Terry Zwigoff really collects 78s). Some other possible candidates for Quarter's semi-obscure cultural signifier:
-WFMU
-Philip K. Dick
-Luc Sante's
Low Life-Postpunk music
-Gospel music (on vinyl)
-Noir (in paperback)
-Knitting
-Krautrock
-Japrock
-Architecture (though he's not an architect)
-Godard (though the movie Plunko is nothing like a Godard movie in any way)
-Lost, weird Westerns (ditto)
-Chet Baker
-The Beats (but not Kerouac)
-Pre-1990 hip-hop
-Soca music
-Steampunk
-Discontinued 'zines
Also, great first post, DanielWR. The skeet shooting thing is golden.