Maycomb Runs on Dunkin
There are two types of coffee in Maycomb.
1. There's coffee with a little c, i.e., the delicious, delicious caffeinated beverage that Jean Louise consumes as if it were water. (We'll raise our grande soy latte to that, Jean Louise.)
2. Then there's Coffee with a capital C, a social function that Jean Louise would rather have nothing to do with, despite the presence of her favorite magical bean drink.
Let's start with little-c coffee first. It's mentioned in the book's very first paragraph, as Jean Louise sips "her breakfast coffee" (1.1), so you know it's important… and not because it's the only thing that gets us—er, Jean Louise—up in the morning. It sets up a minor contrast between Jean Louise and her father, who drinks milk as though he's a child. "Tastes better than coffee" (6.32), Atticus says.
Atticus: you're wrong about everything in this book, aren't you?
Is Jean Louise more refined than Atticus because she drinks coffee? She might think so. She seems to see coffee as a strange symbol of her self-awareness. When Henry points out that Jean Louise doesn't ever finish her second cup of coffee after dinner, she marvels, "Why had he waited fifteen years to tell her?" (4.36) Maybe she isn't as self-aware as she thought?
Also, near the end of the book, she tells Uncle Jack:
"If you tell me that power tends to corrupt and absolute power corrupts absolutely I will throw this coffee at you." (14.133)
PSA, kids: coffee is both highly addictive and a dangerous weapon.
Speaking of dangerous weapons, the capital-C Coffees can also be deadly. Well, maybe not deadly, but they can be so annoying you might want to kill whoever came up with the idea. As Jean Louise describes them:
Coffees were peculiarly Maycombian in nature. They were given for girls who came home. (3.35)
Or, more succinctly: "Horrifyin'" (3.36).
At the Coffee, a bunch of woman who only parrot their husbands' opinions—or have zero opinions if they have no husband—sit around and gossip. It's Jean Louise's worst nightmare.